_repropagationCondition(target) {
    return super._repropagationCondition(target) || this.formElements.every(el => !el.checked);
  }
@enhance FormControlMixin
We need to extend the repropagation prevention conditions here.
Usually form groups with single choice will not repropagate model-value-changed of an option upwards
if this option itself is not the checked one. We want to prevent duplicates. However, for combobox
it is reasonable that an option can become unchecked without another one becoming checked, because
users can enter any text they want, whether it matches an option or not.

Therefore, extend the condition to fail by checking if there is any elements checked. If so, then we
should indeed not repropagate as normally. If there is no elements checked, this will be the only
model-value-changed event that gets received, and we should repropagate it.

@param {FormControlHost} target