Fix flutter run --use-application-binary (#6106)

When using --use-application-binary:

- [x] Stop flutter run from checking for a pubspec.yaml in current directory
- [x] Stop flutter run from invoking pub get
- [x] Set 'shouldBuild' based on --use-application-binary
- [x] Stop requiring 'lib/main.dart' to be present before running.
- [x] Stop building an FLX when launching on Android

packages/flutter_tools/lib/src/ios/simulators.dart

diff --git a/packages/flutter_tools/lib/src/ios/simulators.dart b/packages/flutter_tools/lib/src/ios/simulators.dart
index 981cc3d..49201a3 100644
--- a/packages/flutter_tools/lib/src/ios/simulators.dart
+++ b/packages/flutter_tools/lib/src/ios/simulators.dart
@@ -412,7 +412,8 @@
     String mainPath,
     String route,
     DebuggingOptions debuggingOptions,
-    Map<String, dynamic> platformArgs
+    Map<String, dynamic> platformArgs,
+    bool prebuiltApplication: false
   }) async {
     printTrace('Building ${app.name} for $id.');