Use javascript string escaping in Polymer.html

There's a lot of pitfalls

Fixes #5060

Author: dfreedm

lib/utils/html-tag.html

@@ -52,12 +52,9 @@
      * @return {!HTMLTemplateElement} Constructed HTMLTemplateElement
      */
     Polymer.html = function html(strings, ...values) {
-      // use raw strings to preserve literal escapes in strings
-      /** @type {!Array<string>} */
-      const rawStrings = strings.raw;
       const template = /** @type {!HTMLTemplateElement} */(document.createElement('template'));
       template.innerHTML = values.reduce((acc, v, idx) =>
-        acc + htmlValue(v) + rawStrings[idx + 1], rawStrings[0]);
+        acc + htmlValue(v) + strings[idx + 1], strings[0]);
       return template;
     };
   })();