Add radio-button-looking entries to PopupMenu

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.

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