API android.media.MediaExtractor.getMetrics()

adds the API getMetrics() to android.media.MediaExtractor
includes plumbing through JNI to the underlying mediaextractor
code in frameworks/av.

Tested with some CTS modifications; a more formal set of CTS
updates will be along later.

Bug: 35094936
Test: modified CTS to invoke new API and output results
Change-Id: Id8d56c9c3273b86bbd11e248bdf5004be90b91ef