MediaMuxer:Include info to specify last sample duration

Added ability to set duration of last sample by writing an empty buffer
with EOS flag marked along with presentation time stamp at the end.
Have updated the same and the default behavior in JavaDoc of MediaMuxer.

Bug: 141573686
Bug: 121052341

Test: Document is updated with new information properly.
Change-Id: If15d555e877f0d17040688858673946cf4fe86af