gtk3: add missing libXdamage, explicitly add libXfixes

libXdamage is an optional dependency, however this is needed for XEmbed
tray icons on MATE to work properly. This is already enabled in gtk4.

https://gitlab.gnome.org/GNOME/gtk/-/blob/3.24.36/meson.build#L583
https://gitlab.gnome.org/search?search=xdamage&project_id=665&group_id=8&search_code=true&repository_ref=gtk-3-24

Also explicitly add libXfixes since gtk3 also optionally directly depends
on it.

https://gitlab.gnome.org/GNOME/gtk/-/blob/3.24.36/meson.build#L577

pkgs/development/libraries/gtk/3.x.nix

@@ -145,6 +145,8 @@ stdenv.mkDerivation rec {
     libSM
     libXcomposite
     libXcursor
+    libXdamage
+    libXfixes
     libXi
     libXrandr
     libXrender