Move makeAdjReason() to ProcessRecord

Move the `makeAdjReason()` method from `ProcessStateRecord` to
`ProcessRecord` as part of a refactor. The changes eliminates the
ProcessRecord dependency from ProcessStateRecord.

Bug: 425766486
Test: mmm frameworks/base/services/
Test: atest MockingOomAdjusterTests
Flag: EXEMPT pure refactor

Change-Id: Ic78896f4122bb12eddf924dd0212db8078b2985c