Add support for requestSubmit

[bestter]

This seem a great features that is not supported globally yet.

whatwg/html#4187

https://www.chromestatus.com/feature/6097749495775232

https://html.spec.whatwg.org/multipage/forms.html#dom-form-requestsubmit-dev

[Schweinepriester]

+1

Meanwhile the MDN entry exists: https://caniuse.com/#feat=mdn-api_htmlformelement_requestsubmit