Update parseHTML to use Document.parseHTMLUnsafe where supported (#3185)

Fixes #2682

Author: lukewarlow

src/htmx.js

@@ -525,6 +525,9 @@ var htmx = (function() {
    * @returns {Document}
    */
   function parseHTML(resp) {
+    if ('parseHTMLUnsafe' in Document) {
+      return Document.parseHTMLUnsafe(resp)
+    }
     const parser = new DOMParser()
     return parser.parseFromString(resp, 'text/html')
   }