Rollup merge of #86200 - qwerty01:clone-doc-update, r=JohnTitor

Updates `Clone` docs for `Copy` comparison.

Quite a few people (myself included) have come under the impression that the difference between `Copy` and `Clone` is that `Copy` is cheap and `Clone` is expensive, where the actual difference is that `Copy` constrains the type to bit-wise copying, and `Clone` allows for more expensive operations. The source of this misconception is in the `Clone` docs, where the following line is in the description:

> Differs from `Copy` in that `Copy` is implicit and extremely inexpensive, while `Clone` is always explicit and may or may not be expensive.

The `Clone` documentation page also comes up before the `Copy` page on google when searching for "the difference between `Clone` and `Copy`".

This PR updates the documentation to clarify that "extremely inexpensive" means an "inexpensive bit-wise copy" to hopefully prevent future rust users from falling into this misunderstanding.

Author: JohnTitor

library/core/src/clone.rs

@@ -38,7 +38,7 @@
 
 /// A common trait for the ability to explicitly duplicate an object.
 ///
-/// Differs from [`Copy`] in that [`Copy`] is implicit and extremely inexpensive, while
+/// Differs from [`Copy`] in that [`Copy`] is implicit and an inexpensive bit-wise copy, while
 /// `Clone` is always explicit and may or may not be expensive. In order to enforce
 /// these characteristics, Rust does not allow you to reimplement [`Copy`], but you
 /// may reimplement `Clone` and run arbitrary code.