Real right-to-left pages, and grids that size to their content

A follow-up that makes right-to-left actually work on real sites. The previous update mirrored right-to-left layouts only when a page used the CSS direction property directly - which almost no site does. Real Arabic, Hebrew, Persian and Urdu pages set dir="rtl" on the page, and that path was ignored, so they still came out left-to-right. Now the dir attribute drives the same exact mirror, on the whole page or any part of it. We caught this by rendering real right-to-left pages and looking at them. Alongside it, grids now size their flexible auto and max-content columns to their content, so an item is never squeezed narrower than itself.