Allow activities/services to have app loaders

When a service or activity attaches to a base context, add the
loaders from the application context to the base context. Activity
and service contexts are created before creating the Application
context, so in order to add the app loaders before the component
onCreate method is called, we must add the app loaders to the
component after the app has been initialized.

Bug: 148630842
Test: launch AppResourcesLoaders
Change-Id: I44aa718779c574094590d25fd839f1d9f9134edb