Please add xfixes and xdamage as meson options

https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/blob/0a1d048ee3aac168a4802e315fd13b057498107b/sys/ximage/meson.build#L11 uses dependencies xfixes and xdamage, but those are not declared options in meson_options.txt.

This makes life for packagers hard:

We'd really like to enable all those features. Usually setting -Dauto_features=enabled is enough to enable them all and get loud errors when some dependencies aren't there. But that doesn't work for xfixes and xdamage because they don't appear in meson_options.txt at all.

It would be great if xfixes and xdamage could be added as meson options, so that packagers can turn on loud errors if they aren't available.