[native] Restore ServiceManager#getService() to return IBinder

This fixes a crash in 3p libraries.
A new API ServiceManager#getService2() has been introduced to
work with the Service enum type.

Bug: 354674329
Bug: 355187769
Test: atest servicemanager_test
Test: atest vm_accessor_test
Test: Run the demo app in b/354674329 and check it works
Change-Id: If1e0e9bee6dcd3cfceea69bea58ed5fbe431e81d