Move web-sys tests to the new test framework

Migrate most `web-sys` tests to the new `wasm_bindgen_test` framework with the
new headless browser capabilities!

crates/web-sys/tests/wasm/element.js

@@ -0,0 +1,49 @@
+export function new_div() {
+  return document.createElement("div");
+}
+
+export function new_a() {
+  return document.createElement("a");
+}
+
+export function new_body() {
+  return document.createElement("body");
+}
+
+export function new_br() {
+  return document.createElement("br");
+}
+
+export function new_button() {
+  return document.createElement("button");
+}
+
+export function new_form() {
+  return document.createElement("form");
+}
+
+export function new_head() {
+  return document.createElement("head");
+}
+
+export function new_html() {
+  return document.createElement("html");
+}
+
+export function new_script() {
+  return document.createElement("script");
+}
+
+export function new_span() {
+  return document.createElement("span");
+}
+
+export function new_style() {
+  return document.createElement("style");
+}
+
+export function new_xpath_result() {
+    let xmlDoc = new DOMParser().parseFromString("<root><value>tomato</value></root>", "application/xml");
+    let xpathResult = xmlDoc.evaluate("/root//value", xmlDoc, null, XPathResult.ANY_TYPE, null);
+    return xpathResult;
+}