Bakup and restore communal shared preferences

Create a SharedPreferencesBackupHelper for communal shared preferences
in order to backup and restore communal_shared_prefs.xml file on device.

Bug: b/330945464
Test: dismiss CTA tile; run commands in go/localtransport to backup;
clear `communal_shared_prefs.xml` from the device; CTA shows; restore
with commands; verify CTA tile state is restored as dismissed.
Test: atest CommunalPrefsRepositoryImplTest
Flag: ACONFIG com.android.systemui.communal_hub TEAMFOOD

Change-Id: Ia9e5df9c86ea776899d565bb8c14e5b829627e75