Sync some event interfaces with the HTML spec

Source/core/events/AutocompleteErrorEvent.idl

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 // https://html.spec.whatwg.org/multipage/forms.html#the-autocompleteerrorevent-interface
 
+enum AutocompleteErrorReason { "" /* empty string */, "cancel", "disabled", "invalid" };
+
 [
     Constructor(DOMString type, optional AutocompleteErrorEventInit eventInitDict),
 ] interface AutocompleteErrorEvent : Event {
-    readonly attribute DOMString reason;
+    readonly attribute AutocompleteErrorReason reason;
 };
-