[null-safety] remove enable experiment flags (#69930)

diff --git a/dev/bots/test.dart b/dev/bots/test.dart
index 304e411..7130721 100644
--- a/dev/bots/test.dart
+++ b/dev/bots/test.dart
@@ -383,7 +383,7 @@
   final String examplePath = exampleDirectory.path;
   final bool hasNullSafety = File(path.join(examplePath, 'null_safety')).existsSync();
   final List<String> additionalArgs = hasNullSafety
-    ? <String>['--enable-experiment', 'non-nullable', '--no-sound-null-safety']
+    ? <String>['--no-sound-null-safety']
     : <String>[];
   if (Directory(path.join(examplePath, 'android')).existsSync()) {
     await _flutterBuildApk(examplePath, release: false, additionalArgs: additionalArgs, verifyCaching: verifyCaching);
@@ -589,8 +589,8 @@
 
 Future<void> _runFrameworkTests() async {
   final bq.BigqueryApi bigqueryApi = await _getBigqueryApi();
-  final List<String> soundNullSafetyOptions     = <String>['--enable-experiment=non-nullable', '--null-assertions', '--sound-null-safety'];
-  final List<String> mixedModeNullSafetyOptions = <String>['--enable-experiment=non-nullable', '--null-assertions', '--no-sound-null-safety'];
+  final List<String> soundNullSafetyOptions     = <String>['--null-assertions', '--sound-null-safety'];
+  final List<String> mixedModeNullSafetyOptions = <String>['--null-assertions', '--no-sound-null-safety'];
   final List<String> trackWidgetCreationAlternatives = <String>['--track-widget-creation', '--no-track-widget-creation'];
 
   Future<void> runWidgets() async {
@@ -634,7 +634,6 @@
   Future<void> runPrivateTests() async {
     final List<String> args = <String>[
       'run',
-      '--enable-experiment=non-nullable',
       '--sound-null-safety',
       'test_private.dart',
     ];
@@ -938,13 +937,9 @@
     ]
   );
   await _runWebDebugTest('lib/sound_mode.dart', additionalArguments: <String>[
-    '--enable-experiment',
-    'non-nullable',
     '--sound-null-safety',
   ]);
   await _runWebReleaseTest('lib/sound_mode.dart', additionalArguments: <String>[
-    '--enable-experiment',
-    'non-nullable',
     '--sound-null-safety',
   ]);
 }
@@ -1049,8 +1044,6 @@
       '--debug',
       if (enableNullSafety)
         ...<String>[
-          '--enable-experiment',
-          'non-nullable',
           '--no-sound-null-safety',
           '--null-assertions',
         ],
diff --git a/dev/integration_tests/non_nullable/analysis_options.yaml b/dev/integration_tests/non_nullable/analysis_options.yaml
deleted file mode 100644
index 6bfd455..0000000
--- a/dev/integration_tests/non_nullable/analysis_options.yaml
+++ /dev/null
@@ -1,6 +0,0 @@
-# Exclude lib/main.dart to avoid warnings about the non_nullable
-# experiment before it is enabled.
-analyzer:
-  exclude:
-    - lib/main.dart
-    - test/test_test.dart
diff --git a/dev/integration_tests/non_nullable/lib/main.dart b/dev/integration_tests/non_nullable/lib/main.dart
index 6e0fb3a..fff4692 100644
--- a/dev/integration_tests/non_nullable/lib/main.dart
+++ b/dev/integration_tests/non_nullable/lib/main.dart
@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart=2.10
 import 'package:flutter/material.dart';
 
 String? unused;
diff --git a/dev/integration_tests/non_nullable/pubspec.yaml b/dev/integration_tests/non_nullable/pubspec.yaml
index 36e613c..2405fcd 100644
--- a/dev/integration_tests/non_nullable/pubspec.yaml
+++ b/dev/integration_tests/non_nullable/pubspec.yaml
@@ -5,7 +5,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   flutter:
diff --git a/dev/integration_tests/non_nullable/test/test_test.dart b/dev/integration_tests/non_nullable/test/test_test.dart
index a6f7411..9e26299 100644
--- a/dev/integration_tests/non_nullable/test/test_test.dart
+++ b/dev/integration_tests/non_nullable/test/test_test.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart=2.8
+// @dart = 2.8
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
diff --git a/dev/integration_tests/web/lib/null_assert_main.dart b/dev/integration_tests/web/lib/null_assert_main.dart
index 134720c..80c0a38 100644
--- a/dev/integration_tests/web/lib/null_assert_main.dart
+++ b/dev/integration_tests/web/lib/null_assert_main.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart=2.8
+// @dart = 2.8
 
 import 'null_enabled_api.dart';
 
diff --git a/dev/integration_tests/web/lib/null_enabled_api.dart b/dev/integration_tests/web/lib/null_enabled_api.dart
index 633dac7..c0fc0b6 100644
--- a/dev/integration_tests/web/lib/null_enabled_api.dart
+++ b/dev/integration_tests/web/lib/null_enabled_api.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart=2.10
+// @dart = 2.12
 
 void methodThatAcceptsNonNull(int x) {
   print(x + 2);
diff --git a/dev/integration_tests/web/lib/null_safe_main.dart b/dev/integration_tests/web/lib/null_safe_main.dart
index d5be80d..a5b6068 100644
--- a/dev/integration_tests/web/lib/null_safe_main.dart
+++ b/dev/integration_tests/web/lib/null_safe_main.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart=2.10
+// @dart = 2.12
 
 String? x;
 
diff --git a/dev/integration_tests/web/lib/sound_mode.dart b/dev/integration_tests/web/lib/sound_mode.dart
index a507692..1875c9a 100644
--- a/dev/integration_tests/web/lib/sound_mode.dart
+++ b/dev/integration_tests/web/lib/sound_mode.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart=2.10
+// @dart = 2.12
 
 import 'dart:html' as html;
 
diff --git a/examples/layers/analysis_options.yaml b/examples/layers/analysis_options.yaml
index 03733cd..0620bab 100644
--- a/examples/layers/analysis_options.yaml
+++ b/examples/layers/analysis_options.yaml
@@ -3,8 +3,6 @@
 include: ../../analysis_options.yaml
 
 analyzer:
-  enable-experiment:
-    - non-nullable
   errors:
     always_require_non_null_named_parameters: false # not needed with nnbd
     type_init_formals: false # https://github.com/dart-lang/linter/issues/2192
diff --git a/examples/layers/pubspec.yaml b/examples/layers/pubspec.yaml
index 92c90df..a1b0858 100644
--- a/examples/layers/pubspec.yaml
+++ b/examples/layers/pubspec.yaml
@@ -2,7 +2,7 @@
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.10.0-0.0.dev <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   flutter:
diff --git a/packages/flutter/analysis_options.yaml b/packages/flutter/analysis_options.yaml
index a368eea..eb8a850 100644
--- a/packages/flutter/analysis_options.yaml
+++ b/packages/flutter/analysis_options.yaml
@@ -3,8 +3,6 @@
 include: ../analysis_options.yaml
 
 analyzer:
-  enable-experiment:
-    - non-nullable
   errors:
     always_require_non_null_named_parameters: false # not needed with nnbd
     type_init_formals: false # https://github.com/dart-lang/linter/issues/2192
diff --git a/packages/flutter/test_private/pubspec.yaml b/packages/flutter/test_private/pubspec.yaml
index e06718e..52cac24 100644
--- a/packages/flutter/test_private/pubspec.yaml
+++ b/packages/flutter/test_private/pubspec.yaml
@@ -4,7 +4,7 @@
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.10.0-0.0.dev <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".
@@ -18,6 +18,5 @@
   file: 6.0.0-nullsafety.4 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   platform: 3.0.0-nullsafety.4 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
 
-dev_dependencies:
 
 # PUBSPEC CHECKSUM: b421
diff --git a/packages/flutter/test_private/test/pubspec.yaml b/packages/flutter/test_private/test/pubspec.yaml
index bcbdd32..e53e601 100644
--- a/packages/flutter/test_private/test/pubspec.yaml
+++ b/packages/flutter/test_private/test/pubspec.yaml
@@ -3,7 +3,7 @@
 
 environment:
   # The pub client defaults to an <2.0.0 sdk constraint which we need to explicitly overwrite.
-  sdk: ">=2.10.0-0.0.dev <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".
diff --git a/packages/flutter_driver/analysis_options.yaml b/packages/flutter_driver/analysis_options.yaml
index a368eea..eb8a850 100644
--- a/packages/flutter_driver/analysis_options.yaml
+++ b/packages/flutter_driver/analysis_options.yaml
@@ -3,8 +3,6 @@
 include: ../analysis_options.yaml
 
 analyzer:
-  enable-experiment:
-    - non-nullable
   errors:
     always_require_non_null_named_parameters: false # not needed with nnbd
     type_init_formals: false # https://github.com/dart-lang/linter/issues/2192
diff --git a/packages/flutter_test/analysis_options.yaml b/packages/flutter_test/analysis_options.yaml
index 9adc519..0125e40 100644
--- a/packages/flutter_test/analysis_options.yaml
+++ b/packages/flutter_test/analysis_options.yaml
@@ -3,8 +3,6 @@
 include: ../analysis_options.yaml
 
 analyzer:
-  enable-experiment:
-    - non-nullable
   errors:
     always_require_non_null_named_parameters: false # not needed with nnbd
     unrelated_type_equality_checks: false # https://github.com/dart-lang/linter/issues/2196