am: Extract UID process state into UidStateRecord

Move common UID-level process state, capability, and idle/background
tracking logic from `UidRecord` into a new abstract base class,
`UidStateRecord`. `UidRecord` now extends `UidStateRecord` and delegates
core process state management to the base class.

This refactoring abstracts logic relevant to OomAdjuster decisions and
improves modularity.

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

Change-Id: I9ac99857cf892be6fce9741425041f8914b14d76