Name changes to Media Metrics Keys

The API council noticed that we used keys like "ht" and "wid" which
are more properly namespaced like "android.media.mediacodec.height".
This changes those keys on the generation side of the system; it goes
together with other changes that document the namespaced-names in the
consumption and documentation side of the system.

Bug: 35811992
Test: check 'dumpsys media.metrics', subset of CTS
Change-Id: Ie05a105229ab931a6b14c0157cc642b5d8413dde