Add domain layer for the Multiuser Widget

This change adds the domain layer for the Multiuser Widget.
LoadUsersUseCase maps the  data from the database into the view model.
UpdateUsersUseCase maps the data from the repository into the database.

Bug: b/373645880
Test: atest MultiuserWidgetUnitTests
Flag: android.multiuser.multiuser_widget
Change-Id: Icb9785bb48b895a188a5f34b6924b06f40e9ec31
12 files changed