Radio button activation behavior is not quite right

[domenic]

https://html.spec.whatwg.org/#radio-button-state-(type=radio)

The input activation behavior is to fire an event named input at the element, with the bubbles attribute initialized to true, and then fire an event named change at the element, with the bubbles attribute initialized to true.

However, this test shows that's not the case:

https://jsbin.com/nunawax/1/edit?html,output

Via @liqwid in jsdom/jsdom#2037 (comment)

@liqwid's fix in jsdom was to save the checkedness of the radio button before the legacy-pre-activation behavior steps run, and if that was checked, skip the (input) activation behavior.

[domenic]

Forward-duping to #5000 which was fixed.