Migrate dark theme settings

When restoring settings from a different phone,
UiModeManager did not update the new settings.
Now, the settings are loaded from local storage and changes applied
when the SettingsHelper restores a value of interest

Bug: 138671559
Test: manual test: reset phone1, setup, used data transfer tool to restore from phone2, check dark mode is the same as phone 2
Change-Id: I861bec342b3284e0f398c8610fcc6881c27601a5