Reference GitHub issue in TODO comment (#141582)

[Source](https://github.com/flutter/flutter/pull/133598#discussion_r1446033128)

For future readers.

packages/flutter_tools/lib/src/base/context.dart

@@ -8,7 +8,7 @@ import 'dart:collection';
 import 'package:meta/meta.dart';
 
 // TODO(ianh): We should remove AppContext's mechanism and replace it with
-// passing dependencies directly in constructors, methods, etc.
+// passing dependencies directly in constructors, methods, etc. See #47161.
 
 /// Generates an [AppContext] value.
 ///