Add decode-to-ANativeWindow support to Stagefright.

This change adds support to Stagefright for doing OMX video decoding directly
into buffers dequeued from an ANativeWindow.  It does this by registering the
dequeued buffers with the OMX component using an Android-specific OMX
extension, and then exchanging buffers between the OMX component and the
ANativeWindow.

Change-Id: Ida66f836503255a68d378c6903d96dfe9747ce87