avsamplebuffersink: support CM and CV metas
Submitted by Ilya Konstantinov
avsamplebuffersink currently doesn't use CMSampleBuffer or CVPixelBuffer metas if present in the GstBuffer, instead reconstructing the CVPixelBuffer and CMSampleBuffer.
For buffers coming from other applemedia elements, this needlessly locks them into CPU memory. (And also needlessly does CV and CM housekeeping structure allocations.)