dom: Add missing event handlers

Adding:
* global event handlers,
* window event handlers,
* document and element handlers,
* and support for BeforeUnloadEvent.

Signed-off-by: Piotr Stankiewicz <bionicrift@gmail.com>

components/script/dom/document.rs

@@ -2801,6 +2801,9 @@ impl DocumentMethods for Document {
         // Step 5
         elements
     }
+
+    // https://html.spec.whatwg.org/multipage/#documentandelementeventhandlers
+    document_and_element_event_handlers!();
 }
 
 fn update_with_current_time_ms(marker: &Cell<u64>) {