chore(macros/cssxref): use page-type to detect CSS Functions/Data Types

[wbamberg]

Summary

Replace the use of tags in cssxref with the page type.

Problem

cssxref used tags: we would like to retire tags eventually, and this one is an easy fix since we already have page types for CSS.

Solution

Use page type!

How did you test this change?

Ran yarn dev and added an edit like:

It's a {{cssxref("sign")}} of the {{cssxref("time")}}s.

It's a {{cssxref("sign()")}} of the {{cssxref("<time>")}}s.

....which gave me: