rustdoc: Create `SelfTy` to replace `Generic(kw::SelfUpper)`

Rustdoc often has to special-case `Self` because it is, well, a special
type of generic parameter (although it also behaves as an alias in
concrete impls). Instead of spreading this special-casing throughout the
code base, create a new variant of the `clean::Type` enum that is for
`Self` types.

This is a refactoring that has almost no impact on rustdoc's behavior,
except that `&Self`, `(Self,)`, `&[Self]`, and other similar occurrences
of `Self` no longer link to the wrapping type (reference primitive,
tuple primitive, etc.) as regular generics do. I felt this made more
sense since users would expect `Self` to link to the containing trait or
aliased type (though those are usually expanded), not the primitive that
is wrapping it. For an example of the change, see the docs for
`std::alloc::Allocator::by_ref`.

0 files changed, 0 insertions, 0 deletions