MediaCodec: add getInputFormat() method

Additional input-port format item:

int32: "adaptive-playback"
  video decoders only
  whether codec is configured for adaptive playback.  In this case, if
  codec has max-width/height limits, those limits are also exposed
  (int32: "max-width", "max-height")

Also, getInput/OutputFormat() is now callable in CONFIGURED and
STARTING states, although output format may be missing CSD fields
until INFO_OUTPUT_FORMAT_CHANGED message.

Includes missing OMX support for MP3 software decoder.

Bug: 11785204
Change-Id: I90c7e34ba81c7b81c43641599f3f496e838958c6