Split core's PanicInfo and std's PanicInfo
`PanicInfo` is used in two ways:
1. As argument to the `#[panic_handler]` in `no_std` context.
2. As argument to the [panic hook](https://doc.rust-lang.org/stable/std/panic/fn.set_hook.html) in `std` context.
In situation 1, the `PanicInfo` always has a *message* (of type `fmt::Arguments`), but never a *payload* (of type `&dyn Any`).
In situation 2, the `PanicInfo` always has a *payload* (which is often a `String`), but not always a *message*.
Having these as the same type is annoying. It means we can't add `.message()` to the first one without also finding a way to properly support it on the second one. (Which is what https://github.com/rust-lang/rust/issues/66745 is blocked on.)
It also means that, because the implementation is in `core`, the implementation cannot make use of the `String` type (which doesn't exist in `core`): 0692db1a90/library/core/src/panic/panic_info.rs (L171-L172)
This also means that we cannot easily add a useful method like `PanicInfo::payload_as_str() -> Option<&str>` that works for both `&'static str` and `String` payloads.
I don't see any good reasons for these to be the same type, other than historical reasons.
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This PR is makes 1 and 2 separate types. To try to avoid breaking existing code and reduce churn, the first one is still named `core::panic::PanicInfo`, and `std::panic::PanicInfo` is a new (deprecated) alias to `PanicHookInfo`. The crater run showed this as a viable option, since people write `core::` when defining a `#[panic_handler]` (because they're in `no_std`) and `std::` when writing a panic hook (since then they're definitely using `std`). On top of that, many definitions of a panic hook don't specify a type at all: they are written as a closure with an inferred argument type.
(Based on some thoughts I was having here: https://github.com/rust-lang/rust/pull/115561#issuecomment-1725830032)
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For the release notes:
> We have renamed `std::panic::PanicInfo` to `std::panic::PanicHookInfo`. The old name will continue to work as an alias, but will result in a deprecation warning starting in Rust 1.82.0.
>
> `core::panic::PanicInfo` will remain unchanged, however, as this is now a *different type*.
>
> The reason is that these types have different roles: `std::panic::PanicHookInfo` is the argument to the [panic hook](https://doc.rust-lang.org/stable/std/panic/fn.set_hook.html) in std context (where panics can have an arbitrary payload), while `core::panic::PanicInfo` is the argument to the [`#[panic_handler]`](https://doc.rust-lang.org/nomicon/panic-handler.html) in no_std context (where panics always carry a formatted *message*). Separating these types allows us to add more useful methods to these types, such as `std::panic::PanicHookInfo::payload_as_str()` and `core::panic::PanicInfo::message()`.
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