[Spa] Add ifBlockedOverrideCheckedTo

If ifBlockedOverrideCheckedTo is not null and the current
RestrictedMode is Blocked and Blocked.canOverrideSwitchChecked is
set to true, the switch's checked status will be overridden to this
value.

Also change the RestrictedRepository api to flow.

Bug: 422439682
Flag: EXEMPT new library
Test: unit test
Test: example usage in gallery
Change-Id: I38f833067ff8dd625c4a4c21e4dae2d4ab53e7a9