Add wxListCtrl::IsVisible()

Allow checking if the given item is (at least partially) visible on
screen.

Closes https://github.com/wxWidgets/wxWidgets/pull/1444

Closes #9949.

include/wx/msw/listctrl.h

@@ -154,6 +154,9 @@ public:
     // Gets information about the item
     bool GetItem(wxListItem& info) const;
 
+    // Check if the item is visible
+    bool IsVisible(long item) const wxOVERRIDE;
+
     // Sets information about the item
     bool SetItem(wxListItem& info);