Block communal widget actions until main user is unlocked

This changelist blocks default widget population and other communal
widget-based operations from happening until the main user has been
unlocked.

Test: atest CommunalAppWidgetHostStartableTest
Test: atest DefaultWidgetPopulationTest#testNoInteractionUntilMainUserUnlocked
Test: atest UserRepositoryImplTest#userUnlockedFlow_tracksBroadcastedChanges
Flag: EXEMPT bugfix
Fixes: 385034665
Change-Id: Id96a73f99488b320efaf3b349fe8cad7ebf6ec2c