Auto merge of #79150 - m-ou-se:bye-bye-doc-comment-hack, r=jyn514

Remove all doc_comment!{} hacks by using #[doc = expr] where needed.

This replaces about 200 cases of

`````rust
        doc_comment! {
            concat!("The smallest value that can be represented by this integer type.

# Examples

Basic usage:

```
", $Feature, "assert_eq!(", stringify!($SelfT), "::MIN, ", stringify!($Min), ");",
$EndFeature, "
```"),
            #[stable(feature = "assoc_int_consts", since = "1.43.0")]
            pub const MIN: Self = !0 ^ ((!0 as $UnsignedT) >> 1) as Self;
        }
`````
by
```rust
        /// The smallest value that can be represented by this integer type.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN, ", stringify!($Min), ");")]
        /// ```
        #[stable(feature = "assoc_int_consts", since = "1.43.0")]
        pub const MIN: Self = !0 ^ ((!0 as $UnsignedT) >> 1) as Self;
```

---

**Note:** For a usable diff, make sure to enable 'ignore whitspace': https://github.com/rust-lang/rust/pull/79150/files?diff=unified&w=1

library/core/src/lib.rs

@@ -113,6 +113,7 @@
 #![feature(doc_spotlight)]
 #![feature(duration_consts_2)]
 #![feature(duration_saturating_ops)]
+#![feature(extended_key_value_attributes)]
 #![feature(extern_types)]
 #![feature(fundamental)]
 #![feature(intrinsics)]