OverlayManager updates for upcoming ThemeService

Create the `OverlayManagerInternal` interface to provide a non-Binder API for other system services to call into the `OverlayManagerService`.

This change also includes:
* A new `getEntries` method on `FabricatedOverlay` to filter overlay entries by resource type.
* Allowing `SYSTEM_UID` to register fabricated overlays.

Bug: 333694176
Test: FabricatedOverlaysTest
Flag: android.server.enable_theme_service
Change-Id: I0c4a609db025fbe59f82e816da859f825f9bb7e2