xdg::icon_theme: Add stub

xdg/icon_theme/dirs.ha

@@ -0,0 +1,10 @@
+// Returns the set of directories in which themes should be looked for in order
+// of preference. It will return $HOME/.icons (for backwards compatibility),
+// $XDG_DATA_DIRS/icons, and /usr/share/pixmaps. Applications may further add
+// their own icon directories to this list.
+// 
+// This memory is statically allocated and must not be free'd. It may be
+// overwritten later, so use [[strings::dupall]] to extend its lifetime.
+export fn theme_dirs() ([]str | error) = {
+	// TODO
+};