Show Performance and CPU Profiler screens without app connection (#6567)
* Add Performance and CPU Profiler screens to list of statically available screens
* add OpenSaveButtonGroup
* release notes and changelog
* dart doc
* Update packages/devtools_app/lib/src/screens/performance/performance_screen.dart
Co-authored-by: Daniel Chevalier <danchevalier@google.com>
---------
Co-authored-by: Daniel Chevalier <danchevalier@google.com>