Initial support for restore workspace from last stable db entry.

(see go/play-launcher-plan-launcher-implementation)

1. When Launcher launches for the first time, creates a backup
   of the workspace before sanitizing db entries.
2. Creates a new path in LauncherProvider that triggers workspace
   restore using last stable db entry of the same grid size.
3. When restore from backup created this way, the table will be
   sanitized afterward.

Test:
1. apply on master, build & refresh on physical device
2. factory reset, go through SuW and perform restore
3. exit SuW without signing into Work Profile
4. run following commands in console
adb root
adb remount
adb pull
/data/data/com.google.android.apps.nexuslauncher/databases/launcher.db
sqlite3 ./launcher.db
.tables
SELECT * FROM favorites_bakup;

Bug: 141472083
Change-Id: I8032866a97eb333946d4f62352595d180364126b