core: Account for the globally active input case

Commit afa43154 tried to make sure the focus was properly changed when
calling focus_default_window() by checking the focused window just after
trying to set the focus.

However, the X11 “Inter-Client Communication Conventions Manual” version
2.0 (ICCCM 2 for short) states that some X11 client may want to use a so
called “globally active input” model in which case the client expects
keyboard input and set input focus even when it's not one of its own
window.

To comply with this, when dealing with such clients, mutter will not
change the focus and send a WM_TAKE_FOCUS message instead.

That mechanism will defeat the logic introduced by commit afa43154
because the focused window is not changed in this case. As a result, the
input focus will fallback to the no-focus window.

To avoid this, only check that the focus change occurred for windows
using a synchronous focus model.

v2: Split specific test for "globally active input" model (Florian).
v3: Remove the check for window->unmanaging which is useless (Jonas).

Fixes: afa43154 - "core: Make sure focus_default_window() worked"
Close: https://gitlab.gnome.org/GNOME/mutter/-/issues/1620
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1716>

src/core/workspace.c

@@ -1368,6 +1368,14 @@ try_to_set_focus_and_check (MetaWindow *window,
 {
   meta_window_focus (window, timestamp);
 
+  /* meta_focus_window() will not change focus for clients using the
+   * "globally active input" model of input handling, hence defeating
+   * the assumption that focus should be changed for such windows.
+   * See https://tronche.com/gui/x/icccm/sec-4.html#s-4.1.7
+   */
+  if (meta_window_is_focus_async (window))
+    return TRUE;
+
   /* meta_window_focus() does not guarantee that focus will end up
    * where we expect, it can fail for various reasons, better check
    * it did not actually changed or even left focus to the window we