Listbox/Combobox multi-select features

[cph0]

The multi-select mode adds great features to the components like keeping the drop-down open when selecting items. But it adds/removes the selected item to the value internally. This makes it difficult to extend the behaviour (have to always use single mode).

Would be great if there could be a select all list option. Also the ability to prevent certain items being selected/removed.

Using single mode also means having our own state for opening/closing the drop-down (in order to prevent closing when selecting multiple items). We then lose the click outside to close. Would be great to be able to reuse the internal logic for this.