Auto merge of #73583 - anp:location-eq, r=dtolnay

Auto merge of #73583 - anp:location-eq, r=dtolnay

Derive common traits for panic::Location.

Now that `#[track_caller]` is on track to stabilize, one of the roughest edges of working with it is the fact that you can't do much with `Location` except turn it back into a `(&str, u32, u32)`. Which makes sense because the type was defined around the panic machinery originally passing around that tuple (it has the same layout as Location even).

This PR derives common traits for the type in accordance with the [API guidelines](https://rust-lang.github.io/api-guidelines/interoperability.html#types-eagerly-implement-common-traits-c-common-traits) (those apply to core, right?).

There's a risk here, e.g. if we ever change the representation of `Location` in a way that makes it harder to implement `Ord`, we might not be able to make that change in a backwards-compatible way. I don't think there's any other compatibility hazard here, as the only changes we currently imagine for the type are to add end fields.

cc @rust-lang/libs