Cleanup: Deduplicate implementations of `is_{freeze,copy,sized}_raw`

[Centril]

See: https://doc.rust-lang.org/nightly/nightly-rustc/src/rustc/ty/util.rs.html#1045

This issue has been assigned to @mbStavola via this comment.

[mbStavola]

I'm interested in taking this!

[Centril]

@rustbot assign @mbStavola