feat-bug(aria/combobox-listbox): listbox `[multi]="true"` works only for combobox `readonly` true

### Feature Description

If listbox's `multi=true` and combobox's `readonly=false` we can select only one item. We can only type first letters of countries. And select only one country. We can't use even standard `, ` separator.

If listbox's multi=true and combobox's readonly=true we can open combobox/listbox and select multiple items.

See live: [stackblitz](https://stackblitz.com/edit/stackblitz-starters-28c5sjlj?file=src%2Fcombobox%2Fcombobox.html,src%2Fmain.ts)

### Use Case

It's useful for multiselect, autocomplete