Merge branch 'composite-contextmenu-event'

Fix event object and ID of wxEVT_CONTEXT_MENU sent from parts of a
composite control.

See https://github.com/wxWidgets/wxWidgets/pull/1698

include/wx/window.h

@@ -1514,6 +1514,12 @@ public:
     // Returns true if more idle time is requested.
     virtual bool SendIdleEvents(wxIdleEvent& event);
 
+    // Send wxContextMenuEvent and return true if it was processed.
+    //
+    // Note that the event may end up being sent to a different window, if this
+    // window is part of a composite control.
+    bool WXSendContextMenuEvent(const wxPoint& posInScreenCoords);
+
         // get the handle of the window for the underlying window system: this
         // is only used for wxWin itself or for user code which wants to call
         // platform-specific APIs