Rollup merge of #82434 - jyn514:hash, r=JohnTitor

Add more links between hash and btree collections

- Link from `core::hash` to `HashMap` and `HashSet`
- Link from HashMap and HashSet to the module-level documentation on
  when to use the collection
- Link from several collections to Wikipedia articles on the general
  concept

See also https://github.com/rust-lang/rust/pull/81989#issuecomment-783920840.

library/std/src/collections/hash/map.rs

@@ -17,7 +17,7 @@ use crate::iter::{FromIterator, FusedIterator};
 use crate::ops::Index;
 use crate::sys;
 
-/// A hash map implemented with quadratic probing and SIMD lookup.
+/// A [hash map] implemented with quadratic probing and SIMD lookup.
 ///
 /// By default, `HashMap` uses a hashing algorithm selected to provide
 /// resistance against HashDoS attacks. The algorithm is randomly seeded, and a
@@ -62,6 +62,7 @@ use crate::sys;
 /// The original C++ version of SwissTable can be found [here], and this
 /// [CppCon talk] gives an overview of how the algorithm works.
 ///
+/// [hash map]: crate::collections#use-a-hashmap-when
 /// [hashing algorithms available on crates.io]: https://crates.io/keywords/hasher
 /// [SwissTable]: https://abseil.io/blog/20180927-swisstables
 /// [here]: https://github.com/abseil/abseil-cpp/blob/master/absl/container/internal/raw_hash_set.h

library/std/src/collections/hash/set.rs

@@ -19,7 +19,7 @@ use super::map::{map_try_reserve_error, RandomState};
 // for `bucket.val` in the case of HashSet. I suppose we would need HKT
 // to get rid of it properly.
 
-/// A hash set implemented as a `HashMap` where the value is `()`.
+/// A [hash set] implemented as a `HashMap` where the value is `()`.
 ///
 /// As with the [`HashMap`] type, a `HashSet` requires that the elements
 /// implement the [`Eq`] and [`Hash`] traits. This can frequently be achieved by
@@ -105,6 +105,7 @@ use super::map::{map_try_reserve_error, RandomState};
 /// // use the values stored in the set
 /// ```
 ///
+/// [hash set]: crate::collections#use-the-set-variant-of-any-of-these-maps-when
 /// [`HashMap`]: crate::collections::HashMap
 /// [`RefCell`]: crate::cell::RefCell
 /// [`Cell`]: crate::cell::Cell