Unify media permissions enforcement in framework.

This opens the door to the same consistent logic being shared by
anyone across the OS who wants to enforce storage permissions.

Bug: 126788266
Test: atest --test-mapping packages/apps/MediaProvider
Exempted-From-Owner-Approval: Trivial permissions refactoring
Change-Id: I3107425f8dafa6ba05918bb67c3c0cb5d3899657