awesome: add optional gtk3 support

Add optional gtk3 support to Awesome so that the `beautiful.gtk` module can be
used.

The `beautiful.gtk` uses `lgi` to obtain Gtk via gobject-introspect:

    return require('lgi').Gtk

Since the current build does not include the typelib files needed, the above
call fails.

It turns out that both `gtk3` and `atk` (Accessibility toolkit) are needed, so
this commit adds them as optional build inputs.

Setting `gtk3Support` to `true` e.g. in an overlay will make `beautiful.gtk`
work at the cost of an increased closure size (currently 99.6M vs 223.4M).

Fixes https://github.com/NixOS/nixpkgs/issues/60538

pkgs/applications/window-managers/awesome/default.nix

@@ -6,8 +6,12 @@
 , libxkbcommon, xcbutilxrm, hicolor-icon-theme
 , asciidoctor
 , fontsConf
+, gtk3Support ? false, gtk3 ? null
 }:
 
+# needed for beautiful.gtk to work
+assert gtk3Support -> gtk3 != null;
+
 with luaPackages; stdenv.mkDerivation rec {
   name = "awesome-${version}";
   version = "4.3";
@@ -42,7 +46,8 @@ with luaPackages; stdenv.mkDerivation rec {
                   xorg.libXau xorg.libXdmcp xorg.libxcb xorg.libxshmfence
                   xorg.xcbutil xorg.xcbutilimage xorg.xcbutilkeysyms
                   xorg.xcbutilrenderutil xorg.xcbutilwm libxkbcommon
-                  xcbutilxrm ];
+                  xcbutilxrm ]
+                  ++ stdenv.lib.optional gtk3Support gtk3;
 
   #cmakeFlags = "-DGENERATE_MANPAGES=ON";
   cmakeFlags = "-DOVERRIDE_VERSION=${version}";
@@ -54,7 +59,7 @@ with luaPackages; stdenv.mkDerivation rec {
   LUA_PATH  = "${lgi}/share/lua/${lua.luaversion}/?.lua;;";
 
   postInstall = ''
-    # Don't use wrapProgram or or the wrapper will duplicate the --search
+    # Don't use wrapProgram or the wrapper will duplicate the --search
     # arguments every restart
     mv "$out/bin/awesome" "$out/bin/.awesome-wrapped"
     makeWrapper "$out/bin/.awesome-wrapped" "$out/bin/awesome" \