`panic::Location` `Debug` implementation now prints a byte array

[tgross35]

Since #135054, the Debug implementation for std::panic::Location just prints the byte bag:

fn main() {
    dbg!(std::panic::Location::caller());
}

Stable:

[src/main.rs:2:5] std::panic::Location::caller() = Location {
    file: "src/main.rs",
    line: 2,
    col: 10,
}

Nightly:

[src/main.rs:2:5] std::panic::Location::caller() = Location {
    file_bytes_with_nul: [
        115,
        114,
        99,
        47,
        109,
        97,
        105,
        110,
        46,
        114,
        115,
        0,
    ],
    line: 2,
    col: 10,
}

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=698066c5427dd43cb12df0d2fb5b9300

Originally noticed at #142216.

[tgross35]

@cramertj is there a reason file_bytes_with_nul wasn't made a CStr in #135054? Other than .file() becoming O(n) once it becomes a thin pointer.

Might just need a handwritten debug implementation otherwise.

[tgross35]

Cc @m-ou-se from the review ^