Parse qualified path on struct construction expr and pattern

[dtolnay]

Depending on the outcome of rust-lang/rust#80080. This would be a valid Expr: <Type as Trait>::Assoc::Variant {}

The current parse error is:

error: expected `;`
 --> dev/main.rs:5:45
  |
5 |     let _ = <Type as Trait>::Assoc::Variant {};
  |                                             ^

[dtolnay]

Tracking issue: rust-lang/rust#86935