style: Unify Gecko and Servo EventState/ElementState bits

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

components/style/lib.rs

@@ -89,7 +89,6 @@ pub mod data;
 pub mod dom;
 pub mod dom_apis;
 pub mod driver;
-pub mod element_state;
 #[cfg(feature = "servo")]
 mod encoding_support;
 pub mod error_reporting;