Combobox | add optional layer of collapsable division

[ophirdo]

Hello team,
In Combobox, we can divide options with categories, which is beautiful and very useful. But for Comboboxes with very long lists of options one more layer of division/grouping might be very useful. A picture is worth a thousand words so here are two:

Collapsed groups:

Expanded "Functions & constants" group:

Today we cannot achieve this behavior, not even using optionRenderer, and it can be done in a similar way of the categories property.
Please let me know what you think, I will be happy to contribute.