Roll pubspec forward to new json_schema, matcher and vector_math (#19802)

Pull in new versions of packages with fixes for SCREAMING CAPS CONSTANTS.
diff --git a/examples/platform_channel/pubspec.yaml b/examples/platform_channel/pubspec.yaml
index f75a107..7a39ba5 100644
--- a/examples/platform_channel/pubspec.yaml
+++ b/examples/platform_channel/pubspec.yaml
@@ -7,7 +7,7 @@
   collection: 1.14.6 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   meta: 1.1.5 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   typed_data: 1.1.5 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
-  vector_math: 2.0.6 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
+  vector_math: 2.0.8 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
 
 dev_dependencies:
   flutter_test:
@@ -36,7 +36,7 @@
   json_rpc_2: 2.0.9 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   kernel: 0.3.4 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   logging: 0.11.3+2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
-  matcher: 0.12.2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
+  matcher: 0.12.2+1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   mime: 0.9.6+2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   multi_server_socket: 1.0.2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   node_preamble: 1.4.4 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
@@ -68,4 +68,4 @@
 flutter:
   uses-material-design: true
 
-# PUBSPEC CHECKSUM: 7d5c
+# PUBSPEC CHECKSUM: 06ba