Bug 1773070 - Unify Gecko and Servo EventState/ElementState bits. r=smaug

Add a dom/base/rust crate called just "dom" where we can share these.

Most of the changes are automatic:

  s/mozilla::EventStates/mozilla::dom::ElementState/
  s/EventStates/ElementState/
  s/NS_EVENT_STATE_/ElementState::/
  s/NS_DOCUMENT_STATE_/DocumentState::/

And so on. This requires a new cbindgen version to avoid ugly casts for
large shifts.

Differential Revision: https://phabricator.services.mozilla.com/D148537

dom/html/HTMLInputElement.h

@@ -201,7 +201,7 @@ class HTMLInputElement final : public TextControlElement,
 
   void DestroyContent() override;
 
-  EventStates IntrinsicState() const override;
+  ElementState IntrinsicState() const override;
 
   void SetLastValueChangeWasInteractive(bool);
 
@@ -835,7 +835,7 @@ class HTMLInputElement final : public TextControlElement,
    * that @required attribute applies and the attribute is set; in contrast,
    * Required() returns true whenever @required attribute is set.
    */
-  bool IsRequired() const { return State().HasState(NS_EVENT_STATE_REQUIRED); }
+  bool IsRequired() const { return State().HasState(ElementState::REQUIRED); }
 
   bool HasBeenTypePassword() const { return mHasBeenTypePassword; }