resourcemanager: update the purpose of getClient functions

This change updates the implementation of
getLowestPriorityBiggestClient to limit a single, well-defined purpose.
With that, getClientForResource_l looks for pending removal clients
before calling getLowestPriorityBiggestClient.
Since, there is no change in the functionality or addition
or modifications of ResourceManagerService binder APIs,
this change is unflagged.

Bug: 294886363
Test: atest android.media.misc.cts.ResourceManagerTest
      atest android.media.misc.cts.ResourceManagerMultiTest
      /data/nativetest64/ResourceManagerService_test/ResourceManagerService_test
      /data/nativetest64/ResourceObserverService_test/ResourceObserverService_test
Change-Id: Ia6bfe55541ceb6458be7d0642468604c6089046f