[tool] Exempt federated impl examples from CHANGELOG (flutter#6018)

The example app of a federated example is effectively test-only code, so treat changes to it (other than the one published file) as dev-only for the purposes of deciding what to flag for CHANGELOGs.

script/tool/lib/src/common/package_state_utils.dart

@@ -86,13 +86,29 @@ Future<PackageChangeState> checkPackageChangeState(
         continue;
       }
 
-      // Some other changes don't need version changes, but might benefit from
-      // changelog changes.
+      final bool isUnpublishedExampleChange =
+          _isUnpublishedExampleChange(components, package);
+
+      // Since examples of federated plugin implementations are only intended
+      // for testing purposes, any unpublished example change in one of them is
+      // effectively a developer-only change.
+      if (package.isFederated &&
+          package.isPlatformImplementation &&
+          isUnpublishedExampleChange) {
+        continue;
+      }
+
+      // Anything that is not developer-only might benefit from changelog
+      // changes. This errs on the side of flagging, so that someone checks to
+      // see if it should be mentioned there or not.
       needsChangelogChange = true;
+
+      // Most changes that aren't developer-only need version changes.
       if (
           // One of a few special files example will be shown on pub.dev, but
-          // for anything else in the example publishing has no purpose.
-          !_isUnpublishedExampleChange(components, package)) {
+          // for anything else in the example, publishing isn't necessary (even
+          // if it is relevant to mention in the CHANGELOG for the future).
+          !isUnpublishedExampleChange) {
         needsVersionChange = true;
       }
     }

script/tool/test/common/package_state_utils_test.dart

@@ -231,6 +231,27 @@ void main() {
       expect(state.needsChangelogChange, true);
     });
 
+    test(
+        'requires neither a changelog nor version change for README.md when '
+        'code example is present in a federated plugin implementation',
+        () async {
+      final RepositoryPackage package = createFakePlugin(
+          'a_plugin_android', packagesDir.childDirectory('a_plugin'),
+          extraFiles: <String>['example/lib/main.dart']);
+
+      const List<String> changedFiles = <String>[
+        'packages/a_plugin/a_plugin_android/example/README.md',
+      ];
+
+      final PackageChangeState state = await checkPackageChangeState(package,
+          changedPaths: changedFiles,
+          relativePackagePath: 'packages/a_plugin/a_plugin_android');
+
+      expect(state.hasChanges, true);
+      expect(state.needsVersionChange, false);
+      expect(state.needsChangelogChange, false);
+    });
+
     test(
         'does not requires changelog or version change for build.gradle '
         'test-dependency-only changes', () async {