Base support for `servicestests` under Ravenwood.

As part of upcoming `servicestests` work, this change makes some
general changes.

We don't currently have Mainline stubs included in the Ravenwood
runtime, so this change "hides" references in `PackageManagerInternal`
and `ActivityManagerInternal` while keeping the clients working.

Adds support for `Process.setCanSelfBackground()` to support
ServiceThread.

Adds support for `LocalServices`, along with a new hook to clear out
any registered services between each Ravenwood test.

Bug: 292141694
Test: atest CtsUtilTestCasesRavenwood
Change-Id: Iea3b4a5bf2ebebb34d56cfc76014fc07987cf355