Rework getMetrics() api per API council

Reworking the media metrics getMetrics() calls (currently in MediaCodec,
MediaExtractor, MediaPlayer, and MediaRecorder) to fit new direction
from the API Council.

Drop the MediaMetricsSet that we had in the first round; go back
to a PersistableBundle as the return type. Moves the key definitions
from MediaMetricsSet.MediaCodec to MediaCodec.MetricsConstants

Bug: 37083862
Test: ran the corresponding CTS tests
Change-Id: I7905959ad2109887dd8fd16f0eb2831247abab2a