Rollup merge of #78119 - fusion-engineering-forks:panic-use-as-str, r=Amanieu

Throw core::panic!("message") as &str instead of String.

This makes `core::panic!("message")` consistent with `std::panic!("message")`, which throws a `&str` and not a `String`.

This also makes any other panics from `core::panicking::panic` result in a `&str` rather than a `String`, which includes compiler-generated panics such as the panics generated for `mem::zeroed()`.

---

Demonstration:

```rust
use std::panic;
use std::any::Any;

fn main() {
    panic::set_hook(Box::new(|panic_info| check(panic_info.payload())));

    check(&*panic::catch_unwind(|| core::panic!("core")).unwrap_err());
    check(&*panic::catch_unwind(|| std::panic!("std")).unwrap_err());
}

fn check(msg: &(dyn Any + Send)) {
    if let Some(s) = msg.downcast_ref::<String>() {
        println!("Got a String: {:?}", s);
    } else if let Some(s) = msg.downcast_ref::<&str>() {
        println!("Got a &str: {:?}", s);
    }
}
```

Before:
```
Got a String: "core"
Got a String: "core"
Got a &str: "std"
Got a &str: "std"
```

After:
```
Got a &str: "core"
Got a &str: "core"
Got a &str: "std"
Got a &str: "std"
```

0 files changed, 0 insertions, 0 deletions