LibWebView: Use querySelectorAll to find hoverable tree nodes

We don't need a live HTMLCollection here, so let's use querySelectorAll
to instead iterate over a static NodeList.

Base/res/html/inspector/inspector.js

@@ -53,7 +53,7 @@ inspector.loadDOMTree = tree => {
     let domTree = document.getElementById("dom-tree");
     domTree.innerHTML = atob(tree);
 
-    let domNodes = domTree.getElementsByClassName("hoverable");
+    let domNodes = domTree.querySelectorAll(".hoverable");
 
     for (let domNode of domNodes) {
         domNode.addEventListener("click", event => {