Minor updates to BoundServiceSession

Moving the ownership of the update thread to PSC to simplify
BoundServiceSession.
Moving the updates to be on OomAdjuster thread which should be more
performant than BackgroundThread.

Test: atest FrameworksMockingServicesTests:BoundServiceSessionTests

Flag: EXEMPT refactor

Bug: 416596684
Change-Id: I7664e3d3bc2f8d6ba8df451822df803e0e048ff4
3 files changed