refactor(aria/combobox): Add accessors for pattern properties

Author: adolgachev

src/aria/combobox/combobox.ts

@@ -86,6 +86,9 @@ export class Combobox<V> {
   /** Whether the combobox is expanded. */
   readonly expanded = computed(() => this._pattern.expanded());
 
+  /** The currently highlighted item in the combobox. */
+  readonly highlightedItem = computed(() => this._pattern.highlightedItem());
+
   /** Input element connected to the combobox, if any. */
   readonly inputElement = computed(() => this._pattern.inputs.inputEl());