chore: replace standard with eslint-config-standard and add custom rules (#14636)

* chore: replace standard with eslint-config-standard

This adds support for --cache so linting JS only takes ~1 second and only lints things that changed

It also allows us to add custom linting rules

* chore: add eslint-plugin-mocha and enable the no-exclusive-tests rule

This will block anyone from pushing / merging a `.only` test or describe

spec/fixtures/module/preload-pdf-loaded-in-subframe.js

@@ -1,7 +1,7 @@
 const { ipcRenderer } = require('electron')
 
 document.addEventListener('DOMContentLoaded', (event) => {
-  var subframe = document.getElementById('pdf-frame')
+  var subframe = document.querySelector('#pdf-frame')
   if (subframe) {
     subframe.contentWindow.addEventListener('pdf-loaded', (event) => {
       ipcRenderer.send('pdf-loaded', event.detail)