transcoder: initial version of pause/resume

- Add pause/resume in TranscoderWrapper, save paused state on pause
  and use it to create new transcoder on resume.

Misc fixes:

- TranscoderWrapper::stop should only cancel transcoder if the stop
  is for the currently running job. Scheduler could call stop to
  cancel a job any time.
- Don't hold TranscoderWrapper lock when running event runnable. If
  the runnable calls back into scheduler, and scheduler may call
  transcoder again and deadlock.
- Don't report abort as error if the transcoder is cancelled explicitly.
- Push decoder/encoder start as msgs, so that they could be skipped too
  if the job is cancelled shortly after starts.

Tests:
Add tests for cancel/pause/resume with real transcoder.

bug: 154734285
bug: 154733948
test: unit testing
Change-Id: I2b7d3da69df53b92ab351db455310799ba0e0e8f
diff --git a/services/mediatranscoding/SimulatedTranscoder.h b/services/mediatranscoding/SimulatedTranscoder.h
index 030222b..1c359dd 100644
--- a/services/mediatranscoding/SimulatedTranscoder.h
+++ b/services/mediatranscoding/SimulatedTranscoder.h
@@ -54,7 +54,8 @@
     void start(ClientIdType clientId, JobIdType jobId, const TranscodingRequestParcel& request,
                const std::shared_ptr<ITranscodingClientCallback>& clientCallback) override;
     void pause(ClientIdType clientId, JobIdType jobId) override;
-    void resume(ClientIdType clientId, JobIdType jobId) override;
+    void resume(ClientIdType clientId, JobIdType jobId, const TranscodingRequestParcel& request,
+                const std::shared_ptr<ITranscodingClientCallback>& clientCallback) override;
     void stop(ClientIdType clientId, JobIdType jobId) override;
     // ~TranscoderInterface