Added experimental-emit-debug-metadata flag to flutter frontend server (

flutter#19168)

- Added a --experimental--emit-debug-metadata flag to Flutter frontend server
- False by default
- Passed to the frontend server in the SDK
   - Introduced in change https://dart-review.googlesource.com/c/sdk/+/150181

flutter_frontend_server/lib/server.dart

@@ -28,10 +28,12 @@ class _FlutterFrontendCompiler implements frontend.CompilerInterface {
   _FlutterFrontendCompiler(StringSink output,
       {bool unsafePackageSerialization,
       bool useDebuggerModuleNames,
+      bool emitDebugMetadata,
       frontend.ProgramTransformer transformer})
       : _compiler = frontend.FrontendCompiler(output,
             transformer: transformer,
             useDebuggerModuleNames: useDebuggerModuleNames,
+            emitDebugMetadata: emitDebugMetadata,
             unsafePackageSerialization: unsafePackageSerialization);
 
   @override
@@ -171,6 +173,7 @@ Future<int> starter(
   compiler ??= _FlutterFrontendCompiler(output,
       transformer: ToStringTransformer(transformer, deleteToStringPackageUris),
       useDebuggerModuleNames: options['debugger-module-names'] as bool,
+      emitDebugMetadata: options['experimental-emit-debug-metadata'] as bool,
       unsafePackageSerialization:
           options['unsafe-package-serialization'] as bool);