Use new meta_key_binding_is_reversed() method

Now that mutter gives a way to check if a MetaKeyBinding was marked as
'reversed' or not, gnome-shell does not have to hardcode that a
MetaKeyBinding using a shift modifier is reversed, it can directly check
if the appropriate flag is set.

https://bugzilla.gnome.org/show_bug.cgi?id=732296

js/ui/status/keyboard.js

@@ -473,8 +473,7 @@ const InputSourceIndicator = new Lang.Class({
 
         let popup = new InputSourcePopup(this._mruSources, this._keybindingAction, this._keybindingActionBackward);
         let modifiers = binding.get_modifiers();
-        let backwards = modifiers & Meta.VirtualModifier.SHIFT_MASK;
-        if (!popup.show(backwards, binding.get_name(), binding.get_mask()))
+        if (!popup.show(binding.is_reversed(), binding.get_name(), binding.get_mask()))
             popup.destroy();
     },