Changed returned type of Element.getElementsByClassName to HTMLCollectionOf<Element>

Fixes #543

Author: timocov

baselines/dom.generated.d.ts

@@ -4704,7 +4704,7 @@ interface Element extends Node, ParentNode, NonDocumentTypeChildNode, ChildNode,
     getAttributeNodeNS(namespaceURI: string, localName: string): Attr | null;
     getBoundingClientRect(): ClientRect | DOMRect;
     getClientRects(): ClientRectList | DOMRectList;
-    getElementsByClassName(classNames: string): NodeListOf<Element>;
+    getElementsByClassName(classNames: string): HTMLCollectionOf<Element>;
     getElementsByTagName<K extends keyof HTMLElementTagNameMap>(qualifiedName: K): HTMLCollectionOf<HTMLElementTagNameMap[K]>;
     getElementsByTagName<K extends keyof SVGElementTagNameMap>(qualifiedName: K): HTMLCollectionOf<SVGElementTagNameMap[K]>;
     getElementsByTagName(qualifiedName: string): HTMLCollectionOf<Element>;

inputfiles/addedTypes.json

@@ -610,7 +610,7 @@
                         "getElementsByClassName": {
                             "name": "getElementsByClassName",
                             "override-signatures": [
-                                "getElementsByClassName(classNames: string): NodeListOf<Element>"
+                                "getElementsByClassName(classNames: string): HTMLCollectionOf<Element>"
                             ]
                         },
                         "closest": {