desktop-shell: Activate surface on right click too

This raises the surface to the top on right click as well, which fixes
pop stacking.

https://bugs.freedesktop.org/show_bug.cgi?id=74831
diff --git a/desktop-shell/shell.c b/desktop-shell/shell.c
index fe03420..466ea93 100644
--- a/desktop-shell/shell.c
+++ b/desktop-shell/shell.c
@@ -5852,6 +5852,9 @@
 	weston_compositor_add_button_binding(ec, BTN_LEFT, 0,
 					     click_to_activate_binding,
 					     shell);
+	weston_compositor_add_button_binding(ec, BTN_RIGHT, 0,
+					     click_to_activate_binding,
+					     shell);
 	weston_compositor_add_touch_binding(ec, 0,
 					    touch_to_activate_binding,
 					    shell);