Refresh: Add new font to all pages

[stephaniehobson]

• Over-ride Protocol themes to use the new font on all pages** of the website
• Behind a switch prefixed with M24
• Non-Latin languages should still use their fallback fonts

** Dan needs to review the Firefox pages

[alexgibson]

Some additional things that came up in code review to figure out:

• When the new nav / footer are displayed on OLD pages, what font should they use? Loading both font families might be less jarring in terms of differences from one page to the next, but might be pretty heavy performance wise.
• All Mozilla themed pages will use the new font, but Firefox themed pages will not yet. How should the nav / footer font look on this scenario e.g. on /firefox/new/?

[alexgibson]

See also #15120

[stephaniehobson]

When the new nav / footer are displayed on OLD pages, what font should they use? Loading both font families might be less jarring in terms of differences from one page to the next, but might be pretty heavy performance wise.

The new header and footer should always display with the new fonts -- we don't want them changing from page to page.

All Mozilla themed pages will use the new font, but Firefox themed pages will not yet. How should the nav / footer font look on this scenario e.g. on /firefox/new/?

We're going to put the new fonts on the FIrefox pages and see how they look. Hopefully this works and the performance implications are minimal 🤞 If it's awful maybe there's still a possibility of swapping the font on the body copy even if we keep the headlines in Metropolis to at least lighten the perf implications.