MPEG4Writer:set last frame duration explicitly

Added ability to set duration of last frame by writing an empty buffer with
EOS flag marked along with presentation time stamp at the end.
This timestamp would be used to calculate the duration of the original last frame.

Bug: 141573686
Bug: 121052341

Test: atest android.media.cts.MediaMuxerTest
      atest android.media.cts.MediaRecorderTest
      Unit tested with last sample duration equal to previous sample,
      different from previous sample and zero as well. STTS entries and
      track duration were created as expected.

Change-Id: Ie769dcd013c8c13e69529480d51d124a7ee3b094
Merged-In: Ie769dcd013c8c13e69529480d51d124a7ee3b094

(cherry picked from commit 53f255f5)