In edebug in GUIs, move focus to the selected frame.

In edebug in GUIs, move focus to the selected frame.

Thus when entering edebug, the focus will be moved to the frame with the
source being debugged, and when its finished, the focus will move back.
Commands edebug-visit-eval-list (`E') and edebug-bounce-point (`p') have been
likewise amended.

* src/keyboard.c (readable_events): Handle FOCUS_OUT_EVENT as an invisible
event.  This prevents input-pending-p returning t when one of these events
arrives, and thus obviates an instant termination of sit-for when there's no
"real" event waiting.

* lisp/emacs-lisp/edebug.el (edebug-focus-frame): New function.
(edebug-default-enter, edebug--display-1, edbug-where, edebug-bounce-point)
(edebug-visit-eval-list): Call edebug-focus-frame to move focus into the
window newly selected by edebug-pop-to-buffer.