Reuse views when moving between diagnostic view and editors

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/editor/src/items.rs

@@ -62,6 +62,10 @@ impl ItemHandle for BufferItemHandle {
         Box::new(self.clone())
     }
 
+    fn to_any(&self) -> gpui::AnyModelHandle {
+        self.0.clone().into()
+    }
+
     fn downgrade(&self) -> Box<dyn workspace::WeakItemHandle> {
         Box::new(WeakBufferItemHandle(self.0.downgrade()))
     }