Refactored ContentCaptureService (and infra) to have just one RemoteService.

The initial implementation of AbstractPerUserService assumed the
AbstractRemoteService instances would be created in demand, because that was
the aproach used by Autofill (to minimize the time system service is bound to
the autofill service process).

But for other systems like ContentCapture, it makes more sense to keep a
permanent connection to the remote service, which is running all the time, so
this change changes the infra to allow such permanent connection (which includes
defining an idle timeout value that never unbinds).

Bug: 117779333
Test: atest CtsContentCaptureServiceTestCases CtsAutoFillServiceTestCases

Change-Id: I43386a3fddc56f1dfd6e4e55f243eaa297921123