6818: Add Lifetimes to the HIR r=matklad a=Veykril
This doesn't handle resolve yet as I don't know yet how that will be used. I'll get to that once I start moving the lifetime reference PR to the hir.
This also adds a new `hir` name type for lifetimes and labels, `hir::LifetimeName`.
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>
It's very useful when `pub` is equivalent to "this is crate's public
API", let's enforce this!
Ideally, we should enforce it for local `cargo test`, and only during
CI, but that needs https://github.com/rust-lang/cargo/issues/5034.