Allow deprecating variants

[MDLC01]

This allows deprecating variants, which I did for the two variants that are already deprecated. I will start working on a corresponding typst/typst PR soon. I may wait until typst/typst#6159 is merged first.

With the current system, there is a weird edge case where modifierless variants can be deprecated independently of the symbol itself, although there is no syntactical way to deprecate a modifierless variant in out DSL. I don't think this is too much of an issue. It could even prove useful if we want to change the default variant of symbol (first, mark the modifierless variant as deprecated, then, in a future version, change its value and remove the deprecation), although this will require adding new syntax at this point.

[T0mstone]

Maybe we should generate the part that says something.something is deprecated automatically? That way could just write

@deprecated: use something.else instead

(This would also apply to symbol deprecations ofc)

[MDLC01]

Maybe we should generate the part that says something.something is deprecated automatically?

I thought about it, but I think it is easier to just do it manually. Especially if at some point we need a different message for whatever reason.

[laurmaedje]

typst/typst#6159 is also merged already, so no blockers on the Typst side. :)

[MDLC01]

Will get to it tonight