feat(useOverlay): add isOpen method to check overlay state (#4041)

docs/content/2.composables/use-overlay.md

@@ -66,6 +66,13 @@ Update an overlay using its `id`
 
 Removes the overlay from the DOM using its `id`
 
+- Parameters:
+  - `id`: The identifier of the overlay
+
+### `isOpen(id: symbol): boolean`
+
+Checks if an overlay its open using its `id`
+
 - Parameters:
   - `id`: The identifier of the overlay