1. Manual roll of Dart 021a49e88c...4b9aa2bd7e
dart-lang/sdk@4b9aa2bd7e Revert "[VM/Runtime] Cleanup package config initialization code"
dart-lang/sdk@d44457f79d [Core Libraries] Eliminate the fork in the core libraries.
dart-lang/sdk@29e93bcdbd [VM/Runtime] Cleanup package config initialization code
dart-lang/sdk@07e2921287 [ddc] Cleanup false assumption from subtype check
dart-lang/sdk@62893f9b00 Reland "[vm] Check prefix.loadLibrary is called and returns before prefix members are used."
dart-lang/sdk@ed9112e862 Sort declarations in api_test.dart
dart-lang/sdk@a9bb706ce2 Migration: allow the client to specify which files to analyze/migrate.
dart-lang/sdk@651464c909 Implement the rest of the ArgumentList ASTNode logic in the context type visitor in feature_computer.dart, tests added in feature_computer_test.dart
dart-lang/sdk@c7d9fa996b Clean up some unnecessary code in completion manager
dart-lang/sdk@e11eb2cd08 [nnbd_migration] Fix #42263, tool inserting ! on toString/hashCode

2. Adjusted all flutter libraries.yaml files to account for elimination of the
fork in the Dart core librarie

3. Adjusted flutter gn file to account for elimination of the fork in the
Dart core librarie