Should `core` import the 2021 prelude?

[dpaoliello]

The core crate currently imports the v1 prelude

rust/library/core/src/lib.rs

Lines 285 to 287 in b3df0d7

	#[prelude_import]
	#[allow(unused)]
	use prelude::v1::*;

This recently caused an issue when updating the portable-simd subtree since it was using a trait that was added to the 2021 prelude: #122905 (comment)

Given that core is currently being built as 2021, should it import the 2021 prelude?

cc @workingjubilee @calebzulawski

[Noratrieb]

sounds reasonable

[dpaoliello]

Happy to take care of this.
Do we have a guide or docs on updating the edition that the standard library builds with? Seems like it'd be good to add this as an item to do.

@rustbot claim