Implement Test for Conformance Requirement: conform-web-font-not-accessible-from-other-apps

[garretrieger]

Link to requirement: https://w3c.github.io/IFT/Overview.html#conform-web-font-not-accessible-from-other-apps

[svgeesus]

I think this requires two tests:

1. Show that a font (with the same name as is used in another document, but no associated @font-face is not used in rendering
2. Show that a custom palette in one document is not used by the same chromatic font in another document