MediaCas: add framework APIs

Java API changes to support MediaCas framework.

Also add partial-frame related enums to MediaCodec,
MediaCodecInfo, and MediaExtractor as a way to indicate
a input frame contains partial data.

Test: basic test app and test plugin to execise the code path;
impelenting playback of CAS-secured MPEG2TS streams, including
a Widevine-based CAS plugin, locally modified ExoPlayer and
Android TV Tuner input.

bug: 22804304
Change-Id: Ia4ba1d4046f7588e42bfb21e726390457d2fc8e3