Introduce [Abstract] to mark non-leaf interfaces

Some interfaces like Node, CharacterData and HTMLTableCellElement are never
instantiated directly, only their descendant interfaces are. Those are marked
with [Abstract] to set their type_id to None instead of having dummy values
in the TypeId enums.

components/script/dom/webidls/WorkerGlobalScope.webidl

@@ -2,8 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-// https://www.whatwg.org/html/#workerglobalscope
-//[Exposed=Worker]
+// https://html.spec.whatwg.org/multipage/#workerglobalscope
+[Abstract/*, Exposed=Worker*/]
 interface WorkerGlobalScope : EventTarget {
   [BinaryName="Self_"] readonly attribute WorkerGlobalScope self;
   readonly attribute WorkerLocation location;