gnome-shell calls ibus_input_context_focus_in() in InputMethod.focus_in()
but the event is not actually forwarded to panels and engines in GNOME
Wayland because gnome-shell changes IBus.Capabilite by focus events and
disables IBus.Capabilite.FOCUS when ibus_input_context_focus_in() is called.
IBus.Capabilite is assumed a fixed value per input context in the
first place and it should not be changed by focus events.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/573