Transcoding: Add new AIDL structure TranscodingVideoTrackFormat.

This is needed for client to specify the video format in request
and also letting the service to notify the client of the final format.

Currently TranscodingVideoFormat is implemented as structure parcelable,
but it will be replaced with PersistableBundle later on.

Bug: 145628554
Test: build and flash

Change-Id: I32fcc7a54a2307288a2a03a0b910be30a945dd2b