layout: Introduce support for legacy presentational attributes to selector
matching, and use it for `<input size>` and `<td width>`.

This implements a general framework for legacy presentational attributes
to the DOM and style calculation, so that adding more of them later will
be straightforward.
auto merge of #3622 : pcwalton/servo/html4ever, r=jdm

This implements a general framework for legacy presentational attributes
to the DOM and style calculation, so that adding more of them later will
be straightforward.