Built-in data types: 3-state toggle

Extracted from: https://github.com/comfyanonymous/ComfyUI/issues/8821

### Feature Idea

It would be nice to have a special widget designed for 3 values. It's either a built-in enum or just an argument which is **supposed** to take one of 3 values: `True`, `False`, or "unspecified" aka neither aka `None`.
Visually, might be done like checkboxes where there are 3 familiar states: `☐`, `✓` and `-`. Or like the current toggle, where also a middle state added, which should probably be highlighted with a color.

### Existing Solutions

_No response_

### Other

_No response_