fixup! refactor(cdk-experimental/ui-patterns): track focus by item not index

Author: wagnermaciel

src/cdk-experimental/ui-patterns/behaviors/list-typeahead/list-typeahead.spec.ts

@@ -36,6 +36,7 @@ function getItems(length: number): Signal<TestItem[]> {
   return signal(
     Array.from({length}).map((_, i) => {
       return {
+        index: signal(i),
         searchTerm: signal(`Item ${i}`),
         id: signal(`${i}`),
         disabled: signal(false),