Switch from Arc/RwLock to Rc/RefCell for CodeContextMenu (#22035)

`CodeContextMenu` is always accessed on one thread, so only `Rc`s and
`Rc<RefCell<_>>` are needed. There should be tiny performance benefits
from this. The main benefit of this is that when seeing code accessing a
`RwLock` it would be reasonable to wonder whether it will block. The
only potential downside is the potential for panics due to overlapping
borrows of the RefCells. I think this is an acceptable risk because most
errors of this nature will be local or will be caught by clippy via the
check for holding a RefCell reference over an `await`.

Release Notes:

- N/A

crates/editor/src/element.rs

@@ -1686,7 +1686,7 @@ impl EditorElement {
                     deployed_from_indicator,
                     actions,
                     ..
-                })) = editor.context_menu.read().as_ref()
+                })) = editor.context_menu.borrow().as_ref()
                 {
                     actions
                         .tasks
@@ -1777,7 +1777,7 @@ impl EditorElement {
             if let Some(crate::CodeContextMenu::CodeActions(CodeActionsMenu {
                 deployed_from_indicator,
                 ..
-            })) = editor.context_menu.read().as_ref()
+            })) = editor.context_menu.borrow().as_ref()
             {
                 active = deployed_from_indicator.map_or(true, |indicator_row| indicator_row == row);
             };