Camera3Device: Wait for empty in-flight map when waiting for idle

Currently we only wait for the request queue to be idle, and for
all outstanding buffers to be returned to their queues and their
fences triggered.

But we also need to wait for result metadata to arrive for all
in-flight requests.  This is simplest to check for by monitoring
entries in the in-flight map and signaling idle/active to the
status tracker when the map becomes empty/nonempty.

Bug: 30282459
Change-Id: I34275b0fdb4f279783291d300707ac21a6aa5249