Camera3Device: support shutter after result

Move the code to remove in-flight requests from processCaptureResult
to a separate function so it can be called when the framework
receives a result or a shutter event. An in-flight request will only
be removed when both results and the shutter event arrive in the
case of a successful request.

Also send out results only after the shutter event receives.

Bug: 18135776
Change-Id: I340db1a495c711b0913784d43fd0f144871e4420