[RFA] PR python/13598 - add before_prompt event

[Tom Tromey]

>>>>> "Yao" == Yao Qi <qiyaoltc@gmail.com> writes:

Yao> If you are interested in changes in selected frames, we can add a
Yao> python event selected_frame_changed.  However, as a python api, the
Yao> event should be general enough, IOW, your tool isn't interested in
Yao> temporary frame changes, but other python users may be interested
Yao> in _all_ selected frame changes.

If a general event is implemented, I'll still need a way to filter out
temporary frame changes, to avoid excessive GUI updates.

Tom