Rollup merge of #135080 - Enselic:debug-ptr-metadata, r=thomcc

core: Make `Debug` impl of raw pointers print metadata if present

Make Rust pointers appear less magic by including metadata information in their `Debug` output.

This does not break Rust stability guarantees because `Debug` impl are explicitly exempted from stability:
https://doc.rust-lang.org/std/fmt/trait.Debug.html#stability

> ## Stability
>
> Derived `Debug` formats are not stable, and so may change with future Rust versions. Additionally, `Debug` implementations of types provided by the standard library (`std`, `core`, `alloc`, etc.) are not stable, and may also change with future Rust versions.

Note that a regression test is added as a separate commit to make it clear what impact the last commit has on the output.

Closes #128684 because the output of that code now becomes:

```
thread 'main' panicked at src/main.rs:5:5:
assertion `left == right` failed
  left: Pointer { addr: 0x7ffd45c6fc6b, metadata: 5 }
 right: Pointer { addr: 0x7ffd45c6fc6b, metadata: 3 }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

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