editor: Hide mouse context menu when modal is opened (#29127)

Closes #28787 

The context menu appears before the modal because it is a Deferred
element, which is always displayed above normal elements.

Release Notes:

Previously, the editor context menu appeared before the Command Palette.
This commit ensures the editor context menu is hidden when a modal,
including the Command Palette, is opened.

crates/workspace/src/workspace.rs

@@ -781,6 +781,7 @@ pub enum Event {
         language: &'static str,
     },
     ZoomChanged,
+    ModalOpened,
 }
 
 #[derive(Debug)]
@@ -1051,6 +1052,13 @@ impl Workspace {
         cx.emit(Event::WorkspaceCreated(weak_handle.clone()));
         let modal_layer = cx.new(|_| ModalLayer::new());
         let toast_layer = cx.new(|_| ToastLayer::new());
+        cx.subscribe(
+            &modal_layer,
+            |_, _, _: &modal_layer::ModalOpenedEvent, cx| {
+                cx.emit(Event::ModalOpened);
+            },
+        )
+        .detach();
 
         let bottom_dock_layout = WorkspaceSettings::get_global(cx).bottom_dock_layout;
         let left_dock = Dock::new(DockPosition::Left, modal_layer.clone(), window, cx);