Parse pinned type sugar

[dtolnay]

• Tracking issue: Tracking issue for pin ergonomics rust-lang/rust#130494
• Feature gate: #![feature(pin_ergonomics)]

https://github.com/rust-lang/rust/blob/be01dabfefd2daa4574b974f571c7852085d60cb/tests/ui/async-await/pin-sugar.rs

#![feature(pin_ergonomics)]

trait Trait {
    fn pinned_mut(self: &pin mut Self);
    fn pinned_const(self: &pin const Self);
}