pgtk: Handle (child) frame focusing better

pgtk: Handle (child) frame focusing better

child frames on pgtk are gtk widgets inside the parent surface, rather
than subsurfaces (in wayland ters), and the edit widget is handled
separately from the parent window, so we need to handle signals more
correctly, rather than squinting and assuming an event for the window
is just an event for the edit widget.

* src/gtkutil.c (xg_set_no_accept_focus): set
focus on widget rather than request it on window
* src/pgtkterm.c (pgtk_focus_frame): focus frame on edit_widget
instead
(button_event): Implement focus calls to replace dead X calls