Web designer preview ignores ListBox ColumnWidths

The Web page designer's ListBox preview drew every column at equal width, ignoring the configured ColumnWidths schema. A ListBox with widths such as 25%,25%,50% looked like three equal columns in the designer and only showed the real proportions when run. The designer preview now resolves column widths with the same layout contract as the browser: fixed and percentage widths claim space first, star widths share the remaining space, hidden zero widths take no space, and visible columns keep a 20 px minimum.