Remove unnecessary pub enum glob-imports from `rustc_middle::ty` We used to have an idiom in the compiler where we'd prefix or suffix all the variants of an enum, for example `BoundRegionKind`, with something like `Br`, and then *glob-import* that enum variant directly. `@noratrieb` brought this up, and I think that it's easier to read when we just use the normal style `EnumName::Variant`. This PR is a bit large, but it's just naming. The only somewhat opinionated change that this PR does is rename `BorrowKind::Imm` to `BorrowKind::Immutable` and same for the other variants. I think these enums are used sparingly enough that the extra length is fine. r? `@noratrieb` or reassign