Fix auto submit on non-form elements

[thet]

There are cases where pat-autosubmit is defined on non-form elements, like:

<form>
  <div class="pat-autosubmit">
    <input>
  </div>
</form>

pat-autosubmit invoked a submit event but that never reached the form because that follows not the standard and submit events are meant to be invoked on form elements (or maybe inputs, which did work although I can't derive that behavior from the specs). See: https://developer.mozilla.org/en-US/docs/Web/API/SubmitEvent https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#submitevent

This use case was broken since Patternslib 9.9.7 where we switched to JavaScript submit events from jQuery submit events to fix another problem.

Now the submit event is always invoked on the related form element. Actually the input element where a change happens can be outside the form itself if it is connected with the form via the form attribute.

[thet]

/cc @cornae