Classify dots.c, dots.down, dots.up and dots.v as normal (#1726)

Fixes #713. They were previously classified by Unicode as relations, which caused a '+' sign after one of them to be treated as a unary operator rather than a binary operator. This PR overrides the Unicode classification and classifies them as normal instead, which causes a '+' sign after one of them to be properly treated as a binary operator.

crates/typst-library/src/math/fragment.rs

@@ -216,6 +216,7 @@ impl GlyphFragment {
     pub fn with_id(ctx: &MathContext, c: char, id: GlyphId, span: Span) -> Self {
         let class = match c {
             ':' => Some(MathClass::Relation),
+            '⋯' | '⋱' | '⋰' | '⋮' => Some(MathClass::Normal),
             _ => unicode_math_class::class(c),
         };
         let mut fragment = Self {

tests/typ/math/spacing.typ

@@ -11,7 +11,8 @@ $a not b$ \
 $a+b, a*b$ \
 $sum x, sum(x)$ \
 $sum product x$ \
-$f(x), zeta(x), "frac"(x)$
+$f(x), zeta(x), "frac"(x)$ \
+$a+dots.c+b$
 
 ---
 // Test ignored vs non-ignored spaces.