Fix inputs and outputs for `WebReleaseBundle` (#143023)

Since `WebReleaseBundle` is responsible for copying over the outputs from the subtargets, so it needs to be reflected in inputs and outputs so that things will be recopied when something changes.

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -132,7 +132,7 @@ abstract class Dart2WebTarget extends Target {
 
   @override
   List<Source> get outputs => buildFiles.map(
-    (String file) => Source.pattern('{OUTPUT_DIR}/$file')
+    (String file) => Source.pattern('{BUILD_DIR}/$file')
   ).toList();
 
   @override
@@ -353,9 +353,6 @@ class Dart2WasmTarget extends Dart2WebTarget {
     'dart2wasm.d',
   ];
 
-  @override
-  List<Source> get outputs => const <Source>[];
-
   @override
   Map<String, Object?> get buildConfig => <String, Object?>{
     'compileTarget': 'dart2wasm',
@@ -401,10 +398,13 @@ class WebReleaseBundle extends Target {
   @override
   List<Source> get inputs => <Source>[
     const Source.pattern('{PROJECT_DIR}/pubspec.yaml'),
+    ...buildFiles.map((String file) => Source.pattern('{BUILD_DIR}/$file'))
   ];
 
   @override
-  List<Source> get outputs => <Source>[];
+  List<Source> get outputs => <Source>[
+    ...buildFiles.map((String file) => Source.pattern('{OUTPUT_DIR}/$file'))
+  ];
 
   @override
   List<String> get depfiles => const <String>[

packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart

@@ -220,6 +220,35 @@ void main() {
     ));
   }));
 
+  test('WebReleaseBundle copies over output files when they change', () => testbed.run(() async {
+    final Directory webResources = environment.projectDir.childDirectory('web');
+    webResources.childFile('foo.txt')
+      ..createSync(recursive: true)
+      ..writeAsStringSync('A');
+
+    environment.buildDir.childFile('main.dart.wasm')..createSync()..writeAsStringSync('old wasm');
+    environment.buildDir.childFile('main.dart.mjs')..createSync()..writeAsStringSync('old mjs');
+    await WebReleaseBundle(<WebCompilerConfig>[
+      const WasmCompilerConfig()
+    ]).build(environment);
+    expect(environment.outputDir.childFile('main.dart.wasm')
+      .readAsStringSync(), 'old wasm');
+        expect(environment.outputDir.childFile('main.dart.mjs')
+      .readAsStringSync(), 'old mjs');
+
+    environment.buildDir.childFile('main.dart.wasm')..createSync()..writeAsStringSync('new wasm');
+    environment.buildDir.childFile('main.dart.mjs')..createSync()..writeAsStringSync('new mjs');
+
+    await WebReleaseBundle(<WebCompilerConfig>[
+      const WasmCompilerConfig()
+    ]).build(environment);
+
+    expect(environment.outputDir.childFile('main.dart.wasm')
+      .readAsStringSync(), 'new wasm');
+    expect(environment.outputDir.childFile('main.dart.mjs')
+      .readAsStringSync(), 'new mjs');
+  }));
+
   test('WebEntrypointTarget generates an entrypoint for a file outside of main', () => testbed.run(() async {
     final File mainFile = globals.fs.file(globals.fs.path.join('other', 'lib', 'main.dart'))
       ..createSync(recursive: true)