Since e3e933c4 a keyval can be temporarily remapped to an unused keycode. Due to
some limitations in XTestFakeKeyEvent, the remapping has to be done in the first
xkb group/layout. In case there are two or more keyboard layouts enabled and the
selected keyboard layout is not the first, clutter_keymap_x11_keycode_for_keyval
will fail to retrieve the correct keycode for a remapped keyval. Let's use the
reserved_keycodes map in order to retrieve the correct keycode if needed.
Fixes: https://gitlab.gnome.org/GNOME/mutter/issues/443
(cherry picked from commit e0811ce141)