[PATCH] windowscodecs: Add stub implementation for DDS encoder.

[Esme Povirk (they/them)]

It's a bit strange to use the encoder_info struct without using CommonEncoder.

The interface for CommonDecoder and CommonEncoder was designed to be
usable without the unixlib, and it does seem to decrease the amount of
boilerplate. But, since we need to support IWICDdsEncoder, it probably
doesn't make sense to use it in this case.

We should probably have a fixme in QueryInterface so we can at least
tell when IWICDdsEncoder is used, if not a stub for the interface.