Research options for disposable and leak tracker MVP

[polina-c]

• [ ] Experiment with kernel transformations
• [ ] Prototype library level flag
• [x] Get data from G3 about ChangeNotifier usage
• [ ] Update disposable
• [ ] Update leak_tracker MVP
• [ ] Schedule meeting with language team

[polina-c]

Options for compile time flag: condition for dispatchCreation, flag in pubspec.yaml.

[polina-c]

Closed as duplicate with https://github.com/flutter/devtools/issues/6909