Add wxTextCtrl::PositionToCoords() functions for wxMSW and wxGTK.

The new method allows to find the coordinates in pixels of the given character
in a text control.

Closes #13221.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68450 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/textctrl.h

@@ -167,6 +167,8 @@ protected:
 
     virtual void DoSetValue(const wxString &value, int flags = 0);
 
+    virtual wxPoint DoPositionToCoords(long pos) const;
+
     // wrappers hiding the differences between functions doing the same thing
     // for GtkTextView and GtkEntry (all of them use current window style to
     // set the given characteristic)