Propagate the style attribute of col element to table cells, allowing to migrate column sizes

In HTML, table column can be stylized using the col tag, which can have a span attribute and a style attribute. The span attribute determines the number of rows that the col element relates to, and the style attribute should apply to the whole column.

Confluence uses this to give widths to columns.

We don't have such a concept in XWiki but a good approximation is to propagate the style attribute to the the individual cells of the columns.