Improve spec compliance of validity check #27133
Description
appears incorrect, since the spec only says to fire events on the fields that are invalid, via step 6.1 of https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#statically-validate-the-constraints, which is called into by https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#concept-form-submit
An event is fired on the form element as a whole only as part of the "check validity steps", and those are called into from other places(for example the checkValidity method).
So the implementation of checkValidaty could also be updated to actually fire an event.
see components/script/dom/htmlformelement.rs.