Auto merge of #118841 - compiler-errors:always-copy, r=jackh726

Make most `rustc_type_ir` kinds `Copy` by default

1. There's no reason why `TyKind` and `ConstKind`/`ConstData` can't be `Copy`. This allows us to avoid needing a typed arena for the two types.
2. Simplify some impls into derives.

Author: bors