They work exactly the same as current checkbox-decorated items, but in order to preserve compatibility, separate methods are used, like `add_radio_check_item()`. The other option would have been to add a new parameter at the end of `add_check_item()` and the like, but that would have forced callers to provide the defaults manually.
`is_item_checkable()`, `is_item_checked()` and `set_item_checked()` are used regardless the item is set to look as check box or radio button.
Keeping check in the name adds an additional clue about these facts.
Closes#13055.
(cherry picked from commit ab3b1d9f3e)
