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/CharacterData.webidl

@@ -10,6 +10,7 @@
  * liability, trademark and document use rules apply.
  */
 
+[Abstract]
 interface CharacterData : Node {
   [TreatNullAs=EmptyString] attribute DOMString data;
   readonly attribute unsigned long length;

components/script/dom/webidls/EventTarget.webidl

@@ -6,6 +6,7 @@
  * https://dom.spec.whatwg.org/#interface-eventtarget
  */
 
+[Abstract]
 interface EventTarget {
   void addEventListener(DOMString type,
                         EventListener? listener,

components/script/dom/webidls/HTMLMediaElement.webidl

@@ -5,6 +5,7 @@
 
 // https://www.whatwg.org/html/#htmlmediaelement
 //enum CanPlayTypeResult { "" /* empty string */, "maybe", "probably" };
+[Abstract]
 interface HTMLMediaElement : HTMLElement {
 
   // error state

components/script/dom/webidls/HTMLTableCellElement.webidl

@@ -4,6 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 // https://www.whatwg.org/html/#htmltablecellelement
+[Abstract]
 interface HTMLTableCellElement : HTMLElement {
              attribute unsigned long colSpan;
   //         attribute unsigned long rowSpan;

components/script/dom/webidls/Node.webidl

@@ -7,6 +7,7 @@
  * https://dom.spec.whatwg.org/#interface-node
  */
 
+[Abstract]
 interface Node : EventTarget {
   const unsigned short ELEMENT_NODE = 1;
   const unsigned short ATTRIBUTE_NODE = 2; // historical

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;

components/script/dom/webidls/XMLHttpRequestEventTarget.webidl

@@ -13,7 +13,7 @@
  * http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0.
  */
 
-//[Exposed=(Window,Worker)]
+[Abstract/*, Exposed=(Window,Worker)*/]
 interface XMLHttpRequestEventTarget : EventTarget {
   // event handlers
   attribute EventHandler onloadstart;