It's equivalent to `Ident::from_str_and_span`. The commit also
introduces some more static symbols so that `Ident::new` can be used in
various places instead of `Ident::from_str_and_span`.
The commit also changes `Path::path` from a `&str` to a `Symbol`, which
then allows the lifetime annotation to be removed from `Ty`. Also, the
use of `Symbol` in `Bounds` removes the need for its lifetime
annotation.
9f0080801d