[rpc_binder] Add ARpcServer_newBoundSocket API

This cl is part of the change to replace the init-dependent binder
API ARpcServer_newInitUnixDomain with a more generic version
ARpcServer_newBoundSocket.

Test: atest microdroid_manager_test
Bug: 275729094

Change-Id: I5b8688fb5964e775845a3b878466f8a3cfee2e25