Rename ERROR_CODE_OUTPUT_FORMAT_UNSUPPORTED to
ERROR_CODE_ENCODING_FORMAT_UNSUPPORTED.
This makes the error code more consistent with ERROR_CODE_DECODING_FAILED on the
decoding side. Also, the error code is in the "Encoding errors (4xxx)" section,
so muxer errors probably should be in the "Muxer errors (7xxx)" section instead.
Additionally, no muxer errors currently seem to use
ERROR_CODE_OUTPUT_FORMAT_UNSUPPORTED, so this should be a safe change.
PiperOrigin-RevId: 493322880
c37317222c