Don't send wxActivateEvent for minimized windows in wxMSW

Unexpectedly, minimizing the window by clicking on its taskbar icon resulted
in a wxActivateEvent. This broke the focus handling in wxTLW and resulted in
debug messages about ::SetFocus() failure whenever the window was minimized in
this way.

It also seems that other existing code doesn't take into account the
possibility of getting an "active" activation event when the window is
minimized and this doesn't happen in the other ports, so don't send this event
in wxMSW neither.

Closes #17128.

interface/wx/event.h

@@ -3005,6 +3005,11 @@ public:
         a @c wxEVT_ACTIVATE or @c wxEVT_ACTIVATE_APP event.
     @endEventTable
 
+    @note Until wxWidgets 3.1.0 activation events could be sent by wxMSW when
+    the window was minimized. This reflected the native MSW behaviour but was
+    often surprising and unexpected, so starting from 3.1.0 such events are not
+    sent any more when the window is in the minimized state.
+
     @library{wxcore}
     @category{events}