Function unicode_mathvariant 

pub fn unicode_mathvariant(font: &str) -> &'static str

Normalize a LaTeXML font name to a MathML mathvariant value.

Port of Perl’s unicode_mathvariant($font). Applies normalization: slanted→italic, removes redundant “serif”/“upright”/“medium”, then looks up in the canonical table. Returns “normal” as fallback.