Add setter for cached state within ProcessRecord.

This will be used to forward cached state changes to
WindowProcessController in order to delay configuration changes
from being sent to processes that are cached.

Test: ActivityTaskManagerServiceTests
Test: OomAdjusterTests
Test: ProcessRecordTests
Test: MockingOomAdjusterTests

Bug: 143432064

Change-Id: I28b0be47f5c9601263c7b1fb337543cf68cc160e