Auto merge of #111818 - Urgau:uplift_cmp_nan, r=cjgillot

Uplift `clippy::cmp_nan` lint

This PR aims at uplifting the `clippy::cmp_nan` lint into rustc.

## `invalid_nan_comparisons`

~~(deny-by-default)~~ (warn-by-default)

The `invalid_nan_comparisons` lint checks comparison with `f32::NAN` or `f64::NAN` as one of the operand.

### Example

```rust,compile_fail
let a = 2.3f32;
if a == f32::NAN {}
```

### Explanation

NaN does not compare meaningfully to anything – not even itself – so those comparisons are always false.

-----

Mostly followed the instructions for uplifting a clippy lint described here: rust-lang/rust#99696 (review)

`@rustbot` label: +I-lang-nominated
r? compiler

core/src/num/f32.rs

@@ -403,6 +403,7 @@ impl f32 {
     /// and the stability of its representation over Rust versions
     /// and target platforms isn't guaranteed.
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]
+    #[rustc_diagnostic_item = "f32_nan"]
     pub const NAN: f32 = 0.0_f32 / 0.0_f32;
     /// Infinity (∞).
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]

core/src/num/f64.rs

@@ -401,6 +401,7 @@ impl f64 {
     /// This constant isn't guaranteed to equal to any specific NaN bitpattern,
     /// and the stability of its representation over Rust versions
     /// and target platforms isn't guaranteed.
+    #[rustc_diagnostic_item = "f64_nan"]
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]
     pub const NAN: f64 = 0.0_f64 / 0.0_f64;
     /// Infinity (∞).