handle mouse capture lost event in grid windows and reset the grid to normal state when it happens

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@44606 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/grid.h

@@ -1770,6 +1770,9 @@ public:
     // overridden wxWindow methods
     virtual void Fit();
 
+    // implementation only
+    void CancelMouseCapture();
+
 protected:
     virtual wxSize DoGetBestSize() const;