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