Function strip_first_vec_component 

pub(crate) fn strip_first_vec_component(s: &str) -> Option<String>

For a string like vec4(uv, 0, 0.1) or float3(uv, 0), return uv — the slice up to the first top-level comma inside the constructor. Used by rewrite_tex2dbias to drop the mip-bias arguments.