Add wxActivateEvent::GetActivationReason().

This method is implemented for wxMSW-only currently and allows to check
whether the window is being activated by a mouse click or in some other way
there.

Closes #15516.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74915 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/window.cpp

@@ -4049,7 +4049,10 @@ bool wxWindowMSW::HandleActivate(int state,
 {
     wxActivateEvent event(wxEVT_ACTIVATE,
                           (state == WA_ACTIVE) || (state == WA_CLICKACTIVE),
-                          m_windowId);
+                          m_windowId,
+                          state == WA_CLICKACTIVE
+                            ? wxActivateEvent::Reason_Mouse
+                            : wxActivateEvent::Reason_Unknown);
     event.SetEventObject(this);
 
     return HandleWindowEvent(event);