Migrate Enhanced notifications to SwitchPreferenceCompat

Settings use SwitchPreferenceCompat instead of SwitchPreference in the
future, for new Material 3 UI.

Also clean up unused fields in its controller.

Bug: 306658427
Test: manual - on Notifications page
Change-Id: I0c4dd3f088e68852a1f63ed46447c306f7c0f65a
3 files changed