resourcemanager: move common code into different source.

This change moves all the common code into a separate source
to enable extenstion of resource manager service implementation.
And also, a new creation function is added to enable the same.

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
Merged-In: I70f4776979104f1468e2791bb8e977ab85d9676a
Change-Id: I70f4776979104f1468e2791bb8e977ab85d9676a