Fix rustc_ast_pretty print_qpath resulting in invalid macro input
related https://github.com/rust-lang/rust/issues/76874 (third case)
### Issue:
The input for a procedural macro is incorrect, for the rust code:
```rust
mod m {
pub trait Tr {
type Ts: super::Tu;
}
}
trait Tu {
fn dummy() { }
}
#[may_proc_macro]
fn foo() {
<T as m::Tr>::Ts::dummy();
}
```
the macro will get the input:
```rust
fn foo() {
<T as m::Tr>::dummy();
}
```
Thus `Ts` has disappeared.
### Fix:
This is due to invalid pretty print of qpath. This PR fix it.
4fcb617cbe