Create a singleton all_apex_contributions module type

This will be a container for the the apex_contributions
selected using build flags. This module will be used to query the state of
selected apex contributions instead of a global that can be mutated by
anyone.

It will set a provider containing metadata for source vs prebuilts
selection. To reduce the overhead of a new mutator, this will be done in
the existing `prebuilt_select` mutator.

It will validate that there are no dups (`foo` and `prebuilt_foo` cannot
be both selected)

Bug: 308174923

Test: go test ./android

Change-Id: Ie42999a71f35d70e0e977f5ab07ce451608d9f35