Add .flutter-plugins-dependencies to FlutterBuildSystem; update logic, add tests. (#163278)

I happened to run into this while chasing other bugs, and noticed
`.flutter-plugins-dependencies` is omitted.

I am guessing this is probably quite stale, but something something
[Chesterton's
fence](https://en.wiktionary.org/wiki/Chesterton%27s_fence), and added
tests.

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

@@ -639,15 +639,20 @@ class FlutterBuildSystem extends BuildSystem {
     // We also remove files under .dart_tool, since these are intermediaries
     // and don't need to be tracked by external systems.
     {
+      bool isUnconditionalFile(String path) {
+        return switch (_fileSystem.path.basename(path)) {
+          '.flutter-plugins' || '.flutter-plugins-dependencies' => true,
+          _ when _fileSystem.path.extension(path) == '.xcconfig' => true,
+          _ when _fileSystem.path.split(path).contains('.dart_tool') => true,
+          _ => false,
+        };
+      }
+
       buildInstance.inputFiles.removeWhere((String path, File file) {
-        return path.contains('.flutter-plugins') ||
+        return isUnconditionalFile(path);
-            path.contains('xcconfig') ||
-            path.contains('.dart_tool');
       });
       buildInstance.outputFiles.removeWhere((String path, File file) {
-        return path.contains('.flutter-plugins') ||
+        return isUnconditionalFile(path);
-            path.contains('xcconfig') ||
-            path.contains('.dart_tool');
       });
     }
     trackSharedBuildDirectory(environment, _fileSystem, buildInstance.outputFiles);

packages/flutter_tools/test/general.shard/build_system/build_system_test.dart

@@ -152,6 +152,79 @@ void main() {
     expect(result.outputFiles.single.path, '${environment.buildDir.path}/out');
   });
 
+  group('BuildResult.outputs filtering', () {
+    final TestTarget allFilesTarget =
+        TestTarget((Environment environment) async {})
+          ..name = 'allTextFiles'
+          ..inputs = const <Source>[
+            Source.pattern('{PROJECT_DIR}/*'),
+            Source.pattern('{PROJECT_DIR}/*/*'),
+          ]
+          ..outputs = const <Source>[Source.pattern('{BUILD_DIR}/out')]
+          ..dependencies = <Target>[];
+    late BuildSystem buildSystem;
+
+    setUp(() {
+      buildSystem = setUpBuildSystem(fileSystem);
+    });
+
+    testWithoutContext('normally would update when something has changed', () async {
+      environment.projectDir.childFile('foo.dart').createSync();
+      final BuildResult result = await buildSystem.build(allFilesTarget, environment);
+      expect(
+        result.inputFiles,
+        contains(isA<File>().having((File f) => f.path, 'path', endsWith('foo.dart'))),
+      );
+    });
+
+    testWithoutContext('ignores the .dart_tool directory', () async {
+      environment.projectDir.childDirectory('.dart_tool').createSync();
+      environment.projectDir.childDirectory('.dart_tool').childFile('IGNORE_ME.txt').createSync();
+      final BuildResult result = await buildSystem.build(allFilesTarget, environment);
+      expect(
+        result.inputFiles,
+        isNot(contains(isA<File>().having((File f) => f.path, 'path', endsWith('IGNORE_ME.txt')))),
+      );
+    });
+
+    testWithoutContext('ignores files named .flutter-plugins', () async {
+      environment.projectDir.childFile('.flutter-plugins').createSync();
+      final BuildResult result = await buildSystem.build(allFilesTarget, environment);
+      expect(
+        result.inputFiles,
+        isNot(
+          contains(isA<File>().having((File f) => f.path, 'path', endsWith('.flutter-plugins'))),
+        ),
+      );
+    });
+
+    testWithoutContext('ignores files named .flutter-plugins-dependencies', () async {
+      environment.projectDir.childFile('.flutter-plugins-dependencies').createSync();
+      final BuildResult result = await buildSystem.build(allFilesTarget, environment);
+      expect(
+        result.inputFiles,
+        isNot(
+          contains(
+            isA<File>().having(
+              (File f) => f.path,
+              'path',
+              endsWith('.flutter-plugins-dependencies'),
+            ),
+          ),
+        ),
+      );
+    });
+
+    testWithoutContext('ignores files ending with .xcconfig', () async {
+      environment.projectDir.childFile('foo.xcconfig').createSync();
+      final BuildResult result = await buildSystem.build(allFilesTarget, environment);
+      expect(
+        result.inputFiles,
+        isNot(contains(isA<File>().having((File f) => f.path, 'path', endsWith('.xcconfig')))),
+      );
+    });
+  });
+
   testWithoutContext('Does not re-invoke build if stamp is valid', () async {
     final BuildSystem buildSystem = setUpBuildSystem(fileSystem);