Minimal Phone Mode (part-3)

Introduces a separate database for minimal device mode.

When minimal device mode is enabled/disabled:
1. WellbeingModel receives onChange event from ContentObserver
2. WellbeingModel called DWB's ContentProvider for latest state in
minimal device mode
3. Based on the state, WellbeingModel calls LauncherProvider to put
launcher into normal/minimal mode.
4. When going from normal -> minimal, Launcher switches to a different
database, namely minimal.db, then proceed to database initialization.
5. If the database hasn't been initialized yet, Launcher will call
ContentResolver#openInputStream with following uri:
content://com.google.android.apps.wellbeing.api/launcher_layout
to get the default layout xml.
6. The default layout is then saved in database, and the database is
considered initialized and doesn't need to go through step 5 again in
the future.
7. In case of minimal -> normal, Launcher switches back to its original
database (e.g. launcher.db if the grid size is 5x5), then reload launcher.

Bug: 161462256
Change-Id: I6bafa66440da23281f63454b698ea56b15960022