Rust 1.78 (#11314)

Notable things I've had to fix due to 1.78:
- Better detection of unused items
- New clippy lint (`assigning_clones`) that points out places where assignment operations with clone rhs could be replaced with more performant `clone_into`
Release Notes:

- N/A

crates/editor/src/selections_collection.rs

@@ -69,7 +69,7 @@ impl SelectionsCollection {
         self.next_selection_id = other.next_selection_id;
         self.line_mode = other.line_mode;
         self.disjoint = other.disjoint.clone();
-        self.pending = other.pending.clone();
+        self.pending.clone_from(&other.pending);
     }
 
     pub fn count(&self) -> usize {