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/HTMLLinkElement.cpp

@@ -10,7 +10,6 @@
 #include "mozilla/Attributes.h"
 #include "mozilla/Components.h"
 #include "mozilla/EventDispatcher.h"
-#include "mozilla/EventStates.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/StaticPrefs_dom.h"