Expose TimeManager.suggestExternalTime()

This CL exposes an API that allows system clock time suggestions from an
external clock / time source to be made. The nature of "external" could
be highly form-factor specific. Example, times obtained via the VHAL for
Android Auto OS.

Bug: 157504928
Bug: 177079827
Test: atest android.app.time
CTS-Coverage-Bug: 182275086
Change-Id: I3527e3827a03c1df73fdc1e00c815ad5971a92ca