AppendData:MPEG4Writer&Extractor,MediaAppender

Bug: 154734325

Append media data to an MPEG4File.  Changes were made in
MPEG4Extractor to pass sample offsets of existing data in file to
the writer. MediaAppender class takes cares of parsing and preparing
exisiting MPEG4 file to be added with new data. Data that is present
in the file is not copied again, hence that pass happens fast.
New data is appended at the end of the file.

Test: atest android.mediav2.cts.MuxerTest
Test: atest android.media.cts.MediaMuxerTest
Test: atest android.media.cts.MediaRecorderTest
Test: atest android.media.cts.MediaExtractorTest

Change-Id: I72ef683ec0e5046ef0fcaa996bfba00fe3f596ba