Fix Activity leak via ViewRootImpl

The leak was caused by the ViewRootImpl reusing a cached Vibrator. We now clear the system vibrator in PhoneWindow to avoid this problem.

Bug: 393190314
Flag: com.android.window.flags.clear_system_vibrator
Test: Manual testing
Change-Id: If6e58e6184473e60111e873a77fb23b493df7a10