MPEG4Writer:Optimize number of write(2) calls

Instead of making several write(2) calls to pass length of a video buffer,
club them together in an array and call write(2) once. This reduces the
number of system calls to write a buffer length from 4 to 1(default case),
there by avoiding 75% of user/kernel context switches just for this.
At 240 fps, it would be 240 instead of 960 calls.

Bug: 157160851

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

Change-Id: I7f3c8ecd5f2bccc6c4b87ccd0dc8104f4e98198a