85c38454c0
Move `mir::Field` → `abi::FieldIdx` The first PR for https://github.com/rust-lang/compiler-team/issues/606 This is just the move-and-rename, because it's plenty big already. Future PRs will start using `FieldIdx` more broadly, and concomitantly removing `FieldIdx::new`s.
Please read the rustc-dev-guide chapter on Backend Agnostic Codegen.