gdk/x11: Clear all data in GdkSurfaceX11 finalization

Currently, the GdkSurfaceX11 implementation relies that the upper
layers hid the surface before destruction, and that no
GdkSurfaceClass.compute_resize happened between them. If these
circumstances happened, there would be a compute_size timeout left
dangling after the surface got destroyed, poking at incorrect data
later on. Something that looks like this was reported in the
recent mutter-x11-frames "SSD frames server":

    mutter-x11-frames:423016): GLib-GObject-WARNING **: 19:41:16.869: invalid unclassed pointer in cast to 'GtkWindow'

    Thread 1 "mutter-x11-fram" received signal SIGTRAP, Trace/breakpoint trap.
    g_logv (log_domain=0x7ffff7f7c4f8 "GLib-GObject", log_level=G_LOG_LEVEL_WARNING, format=<optimized out>, args=<optimized out>) at ../../../glib/gmessages.c:1433
    1433	../../../glib/gmessages.c: No such file or directory.
    (gdb) bt
    #0  g_logv (log_domain=0x7ffff7f7c4f8 "GLib-GObject", log_level=G_LOG_LEVEL_WARNING, format=<optimized out>, args=<optimized out>) at ../../../glib/gmessages.c:1433
    #1  0x00007ffff73470ff in g_log (log_domain=log_domain@entry=0x7ffff7f7c4f8 "GLib-GObject", log_level=log_level@entry=G_LOG_LEVEL_WARNING, format=format@entry=0x7ffff7f84da8 "invalid unclassed pointer in cast to '%s'")
        at ../../../glib/gmessages.c:1471
    #2  0x00007ffff7f72892 in g_type_check_instance_cast (type_instance=type_instance@entry=0x5555558e04b0, iface_type=<optimized out>) at ../../../gobject/gtype.c:4144
    #3  0x00007ffff791e77d in toplevel_compute_size (toplevel=<optimized out>, size=0x7fffffffe170, widget=0x5555558e04b0) at ../../../gtk/gtkwindow.c:4227
    #4  0x00007ffff7f4f3b0 in g_closure_invoke (closure=0x555555898cc0, return_value=return_value@entry=0x0, n_param_values=2, param_values=param_values@entry=0x7fffffffdeb0, invocation_hint=invocation_hint@entry=0x7fffffffde30)
        at ../../../gobject/gclosure.c:832
    #5  0x00007ffff7f62076 in signal_emit_unlocked_R
        (node=node@entry=0x55555588feb0, detail=detail@entry=0, instance=instance@entry=0x55555560e990, emission_return=emission_return@entry=0x0, instance_and_params=instance_and_params@entry=0x7fffffffdeb0)
        at ../../../gobject/gsignal.c:3796
    #6  0x00007ffff7f68bf5 in g_signal_emit_valist (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>, var_args=var_args@entry=0x7fffffffe050) at ../../../gobject/gsignal.c:3549
    #7  0x00007ffff7f68dbf in <emit signal ??? on instance 0x55555560e990 [GdkX11Toplevel]> (instance=<optimized out>, signal_id=<optimized out>, detail=detail@entry=0) at ../../../gobject/gsignal.c:3606
    #8  0x00007ffff7a8de96 in gdk_toplevel_notify_compute_size (toplevel=<optimized out>, size=size@entry=0x7fffffffe170) at ../../../gdk/gdktoplevel.c:112
    #9  0x00007ffff7a4b15a in compute_toplevel_size (surface=surface@entry=0x55555560e990 [GdkX11Toplevel], update_geometry=update_geometry@entry=1, width=width@entry=0x7fffffffe220, height=height@entry=0x7fffffffe224)
        at ../../../gdk/x11/gdksurface-x11.c:281
    #10 0x00007ffff7a4c3b2 in compute_size_idle (user_data=0x55555560e990) at ../../../gdk/x11/gdksurface-x11.c:356
    #11 0x00007ffff733f67f in g_main_dispatch (context=0x55555563f6e0) at ../../../glib/gmain.c:3444
    #12 g_main_context_dispatch (context=context@entry=0x55555563f6e0) at ../../../glib/gmain.c:4162
    #13 0x00007ffff733fa38 in g_main_context_iterate (context=0x55555563f6e0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:4238
    #14 0x00007ffff733fcef in g_main_loop_run (loop=loop@entry=0x5555560874a0) at ../../../glib/gmain.c:4438
    #15 0x0000555555557de0 in main (argc=<optimized out>, argv=<optimized out>) at ../src/frames/main.c:68

It perhaps makes sense to warn in these situations, but either way
it sounds like gdk_surface_x11_finalize() could enforce the correct
behavior by ensuring there is no dangling timeouts/data. This commit
does that.

gdk/x11/gdksurface-x11.c

@@ -759,6 +759,8 @@ gdk_x11_surface_finalize (GObject *object)
     }
 
   g_clear_pointer (&impl->surface_is_on_monitor, g_list_free);
+  g_clear_handle_id (&impl->compute_size_source_id, g_source_remove);
+  g_clear_pointer (&impl->toplevel_layout, gdk_toplevel_layout_unref);
 
   g_free (impl->toplevel);