Bug 1850293 - Make validity states non-intrinsic. r=smaug

Add a RAII helper to notify of multiple state changes together for
these.

The UpdateState CustomElementInternals calls that are getting removed
are unnecessary (the state should be up-to-date by then, there's nothing
changing there particularly).

Same for the call in nsGenericHTMLFormElement::UnbindFromTree. ClearForm
already does an state update.

Differential Revision: https://phabricator.services.mozilla.com/D187033

dom/html/HTMLFormElement.h

@@ -80,8 +80,6 @@ class HTMLFormElement final : public nsGenericHTMLElement,
   bool GetValueMissingState(const nsAString& aName) const override;
   void SetValueMissingState(const nsAString& aName, bool aValue) override;
 
-  ElementState IntrinsicState() const override;
-
   // EventTarget
   void AsyncEventRunning(AsyncEventDispatcher* aEvent) override;