Add overlay management functions into OverlayManager

Self-Targeting apps can manage the overlays by the following classes.
* OverlayManager
* OverlayManagerTransaction

For OverlayManager, it provides 2 functions for the app.
* Start a overlay manager transaction
      OverlayManager#beginTransaction()
* List the registered overlays
      OverlayManager#getOverlayInfosForTarget(targetPackage).

For OverlayManagerTransaction, it provides 3 functions for the app.
* register a FabricatedOverlay
      OverlayManagerTransaction#registerFabricatedOverlay
* unregister a FabricatedOverlay
      OverlayManagerTransaction#unregisterFabricatedOverlay
* commit the transaction
      OverlayManagerTransaction#commit

Test: atest \
          OverlayHostTests \
          OverlayDeviceTests \
          SelfTargetingOverlayDeviceTests \
          OverlayRemountedTest \
          FrameworksServicesTests:com.android.server.om \
          CtsContentTestCases:android.content.om.cts \
          idmap2_tests

Bug: 205919743
Change-Id: I3b0b60a30689b3d033f96cfcf02e2f67b480f207