Rollup merge of #123042 - dpaoliello:prelude, r=Nilstrieb

Import the 2021 prelude in the core crate

The `core` crate currently imports the v1 prelude
https://github.com/rust-lang/rust/blob/b3df0d7e5ef5f7dbeeca3fb289c65680ad013f87/library/core/src/lib.rs#L285-L287

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

To make it easier to have a consistent build environment for subtrees and submodules that get included in `core`, we will now import the 2021 prelude into `core`.

Fixes #122912

r? `@Nilstrieb`

Author: workingjubilee