am: Move modifyRawOomAdj to OomAdjuster

The `modifyRawOomAdj` method, used for OOM score adjustments based on
`BIND_ABOVE_CLIENT`, has been moved from `ProcessServiceRecord.java` to
`OomAdjuster.java`.

This method was exclusively used by `OomAdjuster` for OOM score
calculations. Moving it as a static helper in `OomAdjuster`
improves architectural clarity and reduces inter-module
dependencies. Call sites have been updated.

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

Change-Id: I4a6be982820315707e368e923dc31ffae4c893dd