gdk/wayland: Use toplevel surface for activation

gdk/wayland: Use toplevel surface for activation

At the moment of launching/activating an application, the
keyboard focus may be on a transient surface that quickly
disappears after activation. If this happens, and the
compositor handles surface destruction before the activated
application gets to reply, the activation request may be
deemed outdated, and the "demands attention" paths be taken.

Peek the toplevel from the focus surface, as that has larger
guarantees to remain valid for the whole duration of the
operation.

Closes: https://gitlab.gnome.org/GNOME/gtk/-/issues/5820