Math formula in block quotes, footnotes, headers, etc. now adapt to the current document size instead of using a fixed value. The adjustment is based on the eye (ex-height) for consistent optical alignment.

Closes #2145

Better approach than #2149 :

Advantages

• The user can still set math.font.size to a fixed value (globally or temporarily), and then this will be used.
• Otherwise, adjustment is to the ex-height, matching the surrounding font (esp. interesting for inline formulas etc.)

Scenario

{.unnumbered .notoc}
## Regarding Euler's $`e^{\mathrm{i}\pi} + 1 = 0`

Some people say $`e^{\mathrm{i}\pi} + 1 = 0` is one of the most beautiful equation in mathematics.

> But all I want to check here is that $`e^{\mathrm{i}\pi} + 1 = 0` honors the current document font size.[^euler]

[^euler]: And $`e^{\mathrm{i}\pi} + 1 = 0` in a footnote is even smaller.

Run with -u inputters.djot temp/euler-identity.dj -O papersize=a7 -Olandscape=true -c resilient.book

I.e. adaptation between default text (Gentium) and math (Libertinus).

Caveat

• In ex-height adjustment mode (default), performances are slightly degraded. We could do some better font caching, but that's a more general question, somewhat orthogonal to that specific case here. I might open a dedicated issue for discussion.
• Existing tests will fail -- But ideally one would want to make a global pass with all of the proposed math-related PRs for this milestone, after CI/tests: fonts SBL_Hbrw and AmiriQuran's addresses changed and now CI breaks #2297 is also fixed.