psc: Introduce ContentProviderConnectionInternal interface

Abstract ContentProviderConnection by moving its public API
to the new ContentProviderConnectionInternal interface in the
psc (ProcessStateController) package.

Bug: 425766486
Test: m services.core
Test: atest MockingOomAdjusterTests OomAdjusterTests
Test: atest FrameworksServicesTestsRavenwood_ProcessStateController
Flag: EXEMPT pure refactor

Change-Id: I048353f6660f0f43bfe8e95eb2d8ce6b1a02837f