gdiplus: Move the burden of supporting GIF encoding to the WIC backend.

[Dmitry Timoshkov]

Vincent Povirk <madewokherd at gmail.com> wrote:

> I don't have a strong opinion on this, but committing this before we
> have support in WIC seems a bit sideways? What we were doing before
> was broken, but this just makes it broken in a different way. Before,
> we weren't reporting all formats native does, but now we're reporting
> formats we can't encode.
> 
> So, this is just going to break or fix applications at random?

This patch is supposed to print a clear fixme that GIF encoding support
is missing instead of silently failing for no obvious reason.

The referenced bug has numerous other bug reports marked as duplicate
where the failing applications had to be actually debugged in order to
determine a reason of the failure.

-- 
Dmitry.