editor: Include proposed changes editor in navigation history (#18593)

This PR makes it so the proposed changes editor works with the workspace
navigation history.

This allows for easily navigating back to the proposed changes editor
after opening one of the excerpts into the base buffer.

Release Notes:

- N/A

crates/editor/src/proposed_changes_editor.rs

@@ -161,8 +161,28 @@ impl Item for ProposedChangesEditor {
     }
 
     fn added_to_workspace(&mut self, workspace: &mut Workspace, cx: &mut ViewContext<Self>) {
+        self.editor.update(cx, |editor, cx| {
+            Item::added_to_workspace(editor, workspace, cx)
+        });
+    }
+
+    fn deactivated(&mut self, cx: &mut ViewContext<Self>) {
+        self.editor.update(cx, Item::deactivated);
+    }
+
+    fn navigate(&mut self, data: Box<dyn std::any::Any>, cx: &mut ViewContext<Self>) -> bool {
         self.editor
-            .update(cx, |editor, cx| editor.added_to_workspace(workspace, cx));
+            .update(cx, |editor, cx| Item::navigate(editor, data, cx))
+    }
+
+    fn set_nav_history(
+        &mut self,
+        nav_history: workspace::ItemNavHistory,
+        cx: &mut ViewContext<Self>,
+    ) {
+        self.editor.update(cx, |editor, cx| {
+            Item::set_nav_history(editor, nav_history, cx)
+        });
     }
 }