Parse function delegation syntax

[dtolnay]

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RFC: https://github.com/rust-lang/rfcs/pull/3530 Tracking issue: https://github.com/rust-lang/rust/issues/118212

impl Trait for S {
    reuse to_reuse::foo { self }
    reuse Trait::bar { Box::new(self.0) }
    reuse <F as Trait>::baz;
}