ui: Don't break flex layout when using WithRemSize (#12076)

This PR fixes an issue where the flex hierarchy wasn't getting broken by
the use of `WithRemSize`.

Release Notes:

- N/A

crates/ui/src/components/context_menu.rs

@@ -269,7 +269,7 @@ impl Render for ContextMenu {
         let ui_font_size = ThemeSettings::get_global(cx).ui_font_size;
 
         div().occlude().elevation_2(cx).flex().flex_row().child(
-            WithRemSize::new(ui_font_size).child(
+            WithRemSize::new(ui_font_size).flex().child(
                 v_flex()
                     .min_w(px(200.))
                     .track_focus(&self.focus_handle)