psc: move linked list node to ProcessRecordInternal

The `mLinkedNodes` array, used by `OomAdjusterImpl` for its
internal priority queues, is 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: Id89265018801a94ee0ce04d1bc73ff2ddf7c6958