Cache ContentCaptureManager service behind a flag

This service is queried after the application is bound to register
a ContentCaptureOptions callback. Avoid associated ServiceManager
lookups by seeding the application service cache with the appropriate
ContentCaptureManager service handle.

Flag: com.android.server.am.cache_content_capture_service
Test: presubmit
Test: Enable flag + inspect trace for no service_manager startup call
Bug: 414380203
Change-Id: I3637c8bc63cbe82207e25ea3c4ff6d982d45aaae