impl `Copy` for most primitive types explicitly

[liigo]

I can't think of any reason not to do this.

cc #37103

[liigo]

cc https://www.reddit.com/r/rust/comments/58yukd/if_rust_ensures_that_there_is_exactly_one_binding/
Some people are not aware that i32 implements Copy. Many answers on /r/rust said "i32 implements Copy", but it doesn't, at least not explicitly does.

[sinkuu]

Copy is a language built-in trait, so I guess it is automatically implemented for primitive types in the compiler. I don't understand rustc internals at all, but fn copy_conditions is a suspect:)

[liigo]

At docs level, make it clear that they implement Copy

• in the language reference, or
• in the std/core API reference

and, of cause, in the Book.

[ollie27]

I guess this is a duplicate of #25893.

[liigo]

closing as duplicate