Suppress invalid suggestions in destructuring assignment Fixes rust-lang/rust#152694 When destructuring assignment hits a type with `Drop`, the compiler was emitting two broken suggestions: `ref *&mut String::new()` (invalid syntax) and `.clone()` on a temporary (useless). Root cause: the suggestion logic didn't know these bindings were synthetic from assign desugaring. The fix reuses the existing `AssignDesugar` detection in `BindingFinder` to collect those spans and skip both suggestions.