[go_router] Use library prefix for meta (flutter#9434)

We plan to export the `internal` attribute from `package:flutter/foundation.dart`.

Currently, `go_router` has files that import both `package:meta/meta.dart` and `package:flutter/foundation.dart`. This causes [lint failures](https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8712222978061136193/+/u/run_test.dart_for_flutter_plugins_shard_and_subshard_analyze/stdout) when `foundation` exports `internal`:

```
   info - lib/src/match.dart:12:8 - The import of 'package:meta/meta.dart' is unnecessary because all of the used elements are also provided by the import of 'package:flutter/foundation.dart'. Try removing the import directive. - unnecessary_import
   info - lib/src/route.dart:10:8 - The import of 'package:meta/meta.dart' is unnecessary because all of the used elements are also provided by the import of 'package:flutter/foundation.dart'. Try removing the import directive. - unnecessary_import
```

This updates go_router to use a library prefix for `package:meta` in affected files to make the lints happy.

This change is a refactoring and does not affect semantics and is exempt from the test, version change, and CHANGELOG policies.

Part of flutter/flutter#167668

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: loic-sharma

packages/go_router/lib/src/match.dart

@@ -9,7 +9,7 @@ import 'package:collection/collection.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 import 'package:logging/logging.dart';
-import 'package:meta/meta.dart';
+import 'package:meta/meta.dart' as meta;
 
 import 'configuration.dart';
 import 'logging.dart';
@@ -402,7 +402,7 @@ class ShellRouteMatch extends RouteMatchBase {
   ///
   /// This is typically used when pushing or popping [RouteMatchBase] from
   /// [RouteMatchList].
-  @internal
+  @meta.internal
   ShellRouteMatch copyWith({
     required List<RouteMatchBase>? matches,
   }) {
@@ -766,7 +766,7 @@ class RouteMatchList with Diagnosticable {
   /// returns false.
   ///
   /// This method visit recursively into shell route matches.
-  @internal
+  @meta.internal
   void visitRouteMatches(RouteMatchVisitor visitor) {
     _visitRouteMatches(matches, visitor);
   }
@@ -786,7 +786,7 @@ class RouteMatchList with Diagnosticable {
   }
 
   /// Create a new [RouteMatchList] with given parameter replaced.
-  @internal
+  @meta.internal
   RouteMatchList copyWith({
     List<RouteMatchBase>? matches,
     Uri? uri,
@@ -841,7 +841,7 @@ class RouteMatchList with Diagnosticable {
 /// suitable for using with [StandardMessageCodec].
 ///
 /// The primary use of this class is for state restoration and browser history.
-@internal
+@meta.internal
 class RouteMatchListCodec extends Codec<RouteMatchList, Map<Object?, Object?>> {
   /// Creates a new [RouteMatchListCodec] object.
   RouteMatchListCodec(RouteConfiguration configuration)

packages/go_router/lib/src/route.dart

@@ -7,7 +7,7 @@ import 'dart:async';
 import 'package:collection/collection.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
-import 'package:meta/meta.dart';
+import 'package:meta/meta.dart' as meta;
 
 import 'configuration.dart';
 import 'match.dart';
@@ -459,7 +459,7 @@ class GoRoute extends RouteBase {
       extractPathParameters(pathParameters, match);
 
   /// The path parameters in this route.
-  @internal
+  @meta.internal
   final List<String> pathParameters = <String>[];
 
   @override