const POLY_BUILTINS: &[&str];Expand description
Builtins whose return type matches their arg type (HLSL “polymorphic”
element-typed functions). Used by SymbolTable::infer_expr_type —
the same set as BROADCAST_BUILTINS plus a few more pure-passthrough
math functions we don’t need to broadcast-rewrite but whose return
type is “same as arg”.