ServiceConnector impl + migration of RemoteFillService

Original CL ag/5907902 has many merge conflicts so re-posting a trimmed
down version of it.
Initially migrating just the RemoteFillService, with the intention to
migrate others in separate CLs.

Fixes: 122480607
Test: atest CtsAutoFillServiceTestCases
Change-Id: Ibae8b0aa32a7c8283b0fb6eb3c288769b730149a