[winuwp] Add removal warning in config help text (#101086)

packages/flutter_tools/lib/src/features.dart

@@ -216,6 +216,7 @@ const Feature singleWidgetReload = Feature(
 const Feature windowsUwpEmbedding = Feature(
   name: 'Flutter for Windows UWP',
   configSetting: 'enable-windows-uwp-desktop',
+  extraHelpText: 'Warning: Windows UWP support is obsolete and will be removed.',
   master: FeatureChannelSetting(
     available: true,
   ),

packages/flutter_tools/test/general.shard/features_test.dart

@@ -382,6 +382,10 @@ void main() {
       expect(featureFlags.isWindowsUwpEnabled, true);
     });
 
+    testWithoutContext('Flutter Windows UWP desktop config includes removal warning', () {
+      expect(windowsUwpEmbedding.extraHelpText, contains('Windows UWP support is obsolete and will be removed'));
+    });
+
     testWithoutContext('Flutter Windows UWP desktop off by default on stable', () {
       final FeatureFlags featureFlags = createFlags('stable');