debugResolveToolbarItemIds function
The id CNToolbar gives each of items in its payload and its events:
the item's own CNToolbarItem.id, or its kind and its index among the
items of that kind (button#0, menu#1).
Implementation
@visibleForTesting
List<String> debugResolveToolbarItemIds(List<CNToolbarItem> items) =>
_CNToolbarState._resolvedIds(items);