[Bugfix] Convert metadata keys to screaming snake case instead of screaming kebab case in cargo_build_script_runner

[Pagten]

The cargo_build_script_runner currently converts the keys from cargo:KEY=VALUE metadata build script output lines into uppercase. This is not completely correct, however, because Cargo converts those keys to uppercase AND replaces dashes with underscores (effectively doing a conversion to SCREAMING_SNAKE_CASE).

To verify that Cargo is indeed doing the dash-to-underscore conversion, have a look at https://github.com/rust-lang/cargo/blob/10b7d384352f6d9a39f609de44476f815fc792a2/src/cargo/core/compiler/custom_build.rs#L46, which is the code responsible for building the DEP_{crate-name}_{metadata-key} env variables in Cargo. The code is

cmd.env(
    &format!("DEP_{}_{}", super::envify(&name), super::envify(key)),
    value,
);

where super::envify() is defined as

fn envify(s: &str) -> String {
    s.chars()
        .flat_map(|c| c.to_uppercase())
        .map(|c| if c == '-' { '_' } else { c })
        .collect()
}

This PR adds the dash-to-underscore conversion to cargo_build_script_runner.

[illicitonion]

Thanks for the fix, and the clear pointer to cargo's behaviour!