Add wxEventLoop::ScheduleExit().

This method allows to request exiting from the given event loop even if it's
not the currently active one, unlike Exit() which would assert in this case.
With it, it becomes possible to ask the loop to terminate as soon as possible
even if a nested loop is currently running.

See #10258.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74335 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -584,6 +584,7 @@ All:
 - Add new wxFSW_EVENT_ATTRIB and wxFSW_EVENT_UNMOUNT flags (David Hart).
 - Add separate read/written bytes counters and per-direction NOWAIT and WAITALL
   flags to wxSocket (Rob Bresalier).
+- Add wxEventLoop::ScheduleExit() (Rob Bresalier).
 - Add wxProcess::SetPriority() (Marian Meravy).
 - Add wxDir::Close() method (Silverstorm82).
 - Fix wxDateTime::GetWeekOfYear() for the last week of year (aimo).