psc: Move ProcessRecord.mPendingFinishAttach to ProcessRecordInternal

The `mPendingFinishAttach` field and its accessor methods are moved
from `ProcessRecord` to `ProcessRecordInternal`.

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

Change-Id: Id48d42725e8a21b7bd139700bc6f470f01ea0d0b