inputMethod: Keep Capabilite.FOCUS before context.focus_in/focus_out

inputMethod: Keep Capabilite.FOCUS before context.focus_in/focus_out

If context.focus_out() is called *after* context.set_capabilities(0),
The FocusOut D-Bus method is ignored because of no FOCUS capability.
If context.focus_out() is called *before* context.set_capabilities(0),
The 0 capability is set to the next focused context and the
FocusIn D-Bus method is ignored because of no FOCUS capability.
So context.set_capabilities(0) should not be called.

Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6415
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2666>