Added MediaSampleReader interface and an NDK based implementation.

MediaSampleReader is an interface for reading media samples from
multiple tracks independently from each other. Each track maintains
its own time state and reading from other tracks does not effect that.

Test: Unit test.
Bug: 152091443
Change-Id: Ib8c965df5d2a47fc6218ceb80b40d0687fb3b531
13 files changed