Implement wxComboCtrl::GetSizeFromTextSize().

Improve calculation of wxComboCtrl best size which doesn't work correctly for
non-default fonts as shown by r72935. It is still not perfect but better now.

Closes #14825.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72955 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/odcombo.h

@@ -355,6 +355,10 @@ protected:
     // Callback for item width, or -1 for default/undetermined
     virtual wxCoord OnMeasureItemWidth( size_t item ) const;
 
+    // override base implementation so we can return the size for the
+    // largest item
+    virtual wxSize DoGetBestSize() const;
+
     // Callback for background drawing. Flags are same as with
     // OnDrawItem.
     virtual void OnDrawBackground( wxDC& dc, const wxRect& rect, int item, int flags ) const;