[add] accessibility for num

[Mc-Zen]

This PR adds support for adding manual as well as automatic alt texts to standalone numbers, units and quantities for export to accessible formats like PDF UA-1.

This is done by adding a parameter alt that can be one of the following

• a string for specifying a manual alt text
• auto for automatic locale-aware description generation (PRs for adding more translations welcome!)
• a dictionary with the keys times, plus, minus, and power. For English, the corresponding values would be "times", "plus", "minus", and "to the power of".
• a function that receives a dictionary with the keys int, frac, decimal-separator, base, expoenent, abd uncertainty.

Currently available languages:

• English
• German
• French
• Spanish
• Italian

Language addition PRs welcome!

Limitations:

• In text mode, math: false, no alt text is added. This might change in the future.
• For units, the grammar is somewhat limited to a reasonable level, eg currently no difference is made for singular/plural.
• When a num, unit or quantity is inserted into an equation (like $a=#num[2.2e4]$) the alt text of the number will be dismissed since the equation is merged with the outer equation. Maybe Typst will add some modularity in the future.

Todo

• Finish formatting uncertainties before creating the description (in order to avoid things like ".5" in the alt text).

Closes #82

[Mc-Zen]

Hi @SeSodesa ,

I've added support for a distinction between singular/plural! Units in the dictionary are by default singular and the new pluralize dictionary defines a function for each language for how to form the plural. When many units are formed in the same simple way, this can profit from a generic rule. Otherwise, implementing just a dictionary for the plural version is also okay.

The plural is only applied to the last "atomic" unit in the numerator and only when the needs-plural check returns true. For most languages, this function only checks whether the value is 1 or not. French is a bit more particular, the absolute the value needs to be at least 2 for plural.

It would be great if you could update the Finnish translation to make use of these new capabilities!