am: Make computeOomAdjLSP() use ProcessRecordInternal

This change refactors OomAdjuster.computeOomAdjLSP() method to use
ProcessRecordInternal. To achieve that, it replaces direct
`getThread() != null` checks with `isProcessRunning()`, and adds some
abstract methods at ProcessRecordInternal.

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

Change-Id: Id751ea7c4a7e5be53730420819b819c99a0057a1