Refactor the event processing code to add ProcessEventLocally().

This new method can be used to only process the event in this handler or any
handlers connected to it (unlike ProcessEventHere() which doesn't follow the
chain at all), without propagating the event upwards (unlike ProcessEvent()).

Unfortunately implementing this required a field to wxEvent but there doesn't
seem to be any other way to do what we need.

There should be no user-visible changes after this commit, it just paves the
way for the upcoming fixes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64261 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/event.h

@@ -489,8 +489,8 @@ public:
            processed, ProcessEvent() on wxTheApp object is called as the last
            step.
 
-        Notice that steps (3)-(5) are performed in ProcessEventHere() which is
-        called by this function.
+        Notice that steps (2)-(6) are performed in ProcessEventLocally()
+        which is called by this function.
 
         @param event
             Event to process.
@@ -502,14 +502,43 @@ public:
     */
     virtual bool ProcessEvent(wxEvent& event);
 
+    /**
+        Try to process the event in this handler and all those chained to it.
+
+        As explained in ProcessEvent() documentation, the event handlers may be
+        chained in a doubly-linked list. This function tries to process the
+        event in this handler (including performing any pre-processing done in
+        TryBefore(), e.g. applying validators) and all those following it in
+        the chain until the event is processed or the chain is exhausted.
+
+        This function is called from ProcessEvent() and, in turn, calls
+        ProcessEventHere() for each handler in turn. It is not virtual and so
+        cannot be overridden but can, and should, be called to forward an event
+        to another handler instead of ProcessEvent() which would result in a
+        duplicate call to TryAfter(), e.g. resulting in all unprocessed events
+        being sent to the application object multiple times.
+
+        @since 2.9.1
+
+        @param event
+            Event to process.
+        @return
+            @true if this handler of one of those chained to it processed the
+            event.
+     */
+    bool ProcessEventLocally(wxEvent& event);
+
     /**
         Try to process the event in this event handler.
 
-        This method is called from ProcessEvent(), please see the detailed
-        description of the event processing logic there.
+        This method is called from ProcessEventLocally() and thus,
+        indirectly, from ProcessEvent(), please see the detailed description of
+        the event processing logic there.
 
         It is @em not virtual and so may not be overridden.
 
+        @since 2.9.1
+
         @param event
             Event to process.
         @return