Form validation for required radio buttons is broken

[m-akinc]

🐛 Bug Report

1. required on a radio button does not take other buttons in the group into account. It will result in a validation error if that specific radio is unchecked. Instead, it should only report a validation error if none of the radio buttons in the radio button group are checked.

2. Validity is only updated when the value or checked state changes, so if a radio button with required is initially unchecked and remains unchecked, it will remain marked valid, even though it violates the required constraint.

Note that the expected behavior of required radio buttons is that required specified on any radio button applies to the group of buttons as a whole.