"Select All" functionality

Hi, 

I am using multiselect-combo-box-flow version 2.5.0 with Vaadin 14. 

I am looking to add "Select All" functionality for my multi-select drop-down. I had a look at the available APIs but I don't see any related to "Select All" functionality. Is this functionality possible to achieve with my version or any other version? Any help would be greatly appreciated.

Thanks,
Sakthi

