Function tvix_glue::tvix_build::calculate_pass_as_file_env

fn calculate_pass_as_file_env(k: &str) -> (String, String)

For a given key k in a derivation environment that’s supposed to be passed as file, calculate the ${k}Path key and filepath value that it’s being replaced with while preparing the build. The filepath is /build/.attrs-${nixbase32(sha256(key)).