metrics on latency through codecs

track the latency for frames to go through the codec and return to the
caller. Provide min/max/avg/N information for the total and for the
last couple hundred frames. Histogram data is collected, but not yet
emitted.

Bug: 64022743
Test: dumpsys media.metrics
Change-Id: I954f0048997c8f65931c4faa678666eec59aaf86