Function rename_word_call 

pub(crate) fn rename_word_call(src: &str, from: &str, to: &str) -> String

Rename <from>( → <to>( at every word boundary. Used to alias HLSL builtins that WGSL spells differently (sat → saturate, rsqrt → inverseSqrt). Differs from a plain replace: a preset local frsqrt = q1 won’t pick up an unwanted frinverseSqrt = q1 rewrite because we require a non-identifier byte (or start of source) to the left of the match.