Use Babel and ES6 in docs JS files (#31607)

* Pass docs js through Babel

* Use ES6 in docs js

* Only run babel on src files

* Allow babel in Hugo

* Update scripts.html

* Inherit from the root .eslintrc.json

* Use `Array.from`

* Drop Babel from docs

* Prefer template

* replace IIFE with arrow functions

Co-authored-by: XhmikosR <xhmikosr@gmail.com>
Co-authored-by: GeoSot <geo.sotis@gmail.com>

site/content/docs/5.1/examples/dashboard/dashboard.js

@@ -1,14 +1,14 @@
 /* globals Chart:false, feather:false */
 
-(function () {
+(() => {
   'use strict'
 
   feather.replace({ 'aria-hidden': 'true' })
 
   // Graphs
-  var ctx = document.getElementById('myChart')
+  const ctx = document.getElementById('myChart')
   // eslint-disable-next-line no-unused-vars
-  var myChart = new Chart(ctx, {
+  const myChart = new Chart(ctx, {
     type: 'line',
     data: {
       labels: [