[SuperEditor] - Composer preferences needs to change its notifier behavior to match Editable expectations

[matthew-carroll]

Currently the ComposerPreferences inside of MutableDocumentComposer has its own ChangeNotifier implementation.

This is a problem because the entire MutableDocumentComposer is an Editable, and therefore should be pausing and resuming all change notifications based on the Editor pipeline.

Update the composer preferences to pause and resume notifications as needed.