Color Knowledge content

Intended content:

**MVP**

* Glossary: Color fonts
* Topic: Color fonts
* Article: Introducing type > Introducing color fonts
* Sibling to https://fonts.google.com/knowledge/introducing_type/introducing_variable_fonts
* If possible, route people here from 'Show only color' checkbox
* Define color fonts (drawing on IUC45 content)
* Discuss capabilities
* Exhibit Emoji, Arabic, etc
* Note browser support issues and that GF API hides these to an extent

**Post-MVP**

Some sort of new section for eng-focused content. "Under the hood" ?

Note to self: use https://github.com/rsheeter/svg_seq to generate svgs of "real" color fonts to use where Knowledge expects svgs, such as for thumbnails.