Invalidate wxDataViewCtrl bests widths on expand/collapse.

The best column widths are computed from "realized" items that are
available as rows in wxDataViewCtrl. This information changes when a
previously collapsed node is expanded and new items become available for
column width calculation.

Fixes #14167.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71334 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775