Auto merge of #115694 - clarfonthey:std-hash-private, r=dtolnay

Add `std:#️⃣:{DefaultHasher, RandomState}` exports (needs FCP)

This implements rust-lang/libs-team#267 to move the libstd hasher types to `std::hash` where they belong, instead of `std::collections::hash_map`.

<details><summary>The below no longer applies, but is kept for clarity.</summary>
This is a small refactor for #27242, which moves the definitions of `RandomState` and `DefaultHasher` into `std::hash`, but in a way that won't be noticed in the public API.

I've opened rust-lang/libs-team#267 as a formal ACP to move these directly into the root of `std::hash`, but for now, they're at least separated out from the collections code in a way that will make moving that around easier.

I decided to simply copy the rustdoc for `std::hash` from `core::hash` since I think it would be ideal for the two to diverge longer-term, especially if the ACP is accepted. However, I would be willing to factor them out into a common markdown document if that's preferred.
</details>

library/core/src/ptr/mod.rs

@@ -1921,8 +1921,7 @@ pub fn addr_eq<T: ?Sized, U: ?Sized>(p: *const T, q: *const U) -> bool {
 /// # Examples
 ///
 /// ```
-/// use std::collections::hash_map::DefaultHasher;
-/// use std::hash::{Hash, Hasher};
+/// use std::hash::{DefaultHasher, Hash, Hasher};
 /// use std::ptr;
 ///
 /// let five = 5;