As is, ClutterImage is not really useful, it only serves for rendering a
CoglTexture as an actor. Shell, has a subclass that adds more features
that unfortunately cannot be upstreamed without bringing more gdk-pixbuf
usage inside libmutter, eg implementing GIcon/GLoadableIcon.
It also has requirements based on whether the image is symbolic or not.
Things that Clutter so far doesn't care about.
So just remove ClutterImage & let shells re-implement it themselves if
needed based on their needs.
Note, that once we have ClutterSnapshot, it should be straightforward to
write a custom actor that renders a CoglTexture or so.
This "un"fortunately means getting rid of various interactive tests that
either didn't compile at all or are not useful as is, like all the
remaining interactive tests.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4133>
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