chore: replace metalsmith-prism with highlight.js (#4493)

Remove a metalsmith plugin that hasn't been updated recently. This has
several advantages:

* Removes some vulnerabilities the GitHub UI is complaining about.
* Eliminates an error message when building involving prism.
* Uses the same highlighting library as the docs, setting the stage for
  possible consolidation and/or alignment.

Author: Trott

build.js

@@ -18,7 +18,6 @@ const discoverHelpers = require('metalsmith-discover-helpers');
 const discoverPartials = require('metalsmith-discover-partials');
 const layouts = require('metalsmith-layouts');
 const markdown = require('@metalsmith/markdown');
-const prism = require('metalsmith-prism');
 const permalinks = require('@metalsmith/permalinks');
 const pagination = require('metalsmith-yearly-pagination');
 const defaultsDeep = require('lodash.defaultsdeep');
@@ -46,13 +45,10 @@ const nodejsVersionsContent = require('fs')
   .readFileSync('./source/nodejsVersions.md')
   .toString();
 
-// Set up the Markdown renderer that we'll use for our Metalsmith build process,
-// with the necessary adjustments that we need to make in order to have Prism
-// work.
+// Set up the Markdown renderer that we'll use for our Metalsmith build process.
 const renderer = new marked.Renderer();
 renderer.heading = anchorMarkdownHeadings;
 const markedOptions = {
-  langPrefix: 'language-',
   renderer
 };
 
@@ -162,7 +158,6 @@ function buildLocale(source, locale, opts) {
     )
     .use(markdown(markedOptions))
     .use(githubLinks({ locale, site: i18nJSON(locale) }))
-    .use(prism())
     // Set pretty permalinks, we don't want .html suffixes everywhere.
     .use(
       permalinks({

layouts/partials/footer.hbs

@@ -36,3 +36,5 @@
 </footer>
 
 <script src="/static/js/main.js" async defer></script>
+<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.5.0/highlight.min.js" integrity="sha512-BNc7saQYlxCL10lykUYhFBcnzdKMnjx5fp5s5wPucDyZ7rKNwCoqJh1GwEAIhuePEK4WM9askJBRsu7ma0Rzvg==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
+<script>hljs.highlightAll();</script>

layouts/partials/html-head.hbs

@@ -7,6 +7,7 @@
 
   <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Source+Sans+Pro:400,600&display=fallback">
   <link rel="stylesheet" href="/static/css/styles.css">
+  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.5.0/styles/a11y-dark.min.css" integrity="sha512-Vj6gPCk8EZlqnoveEyuGyYaWZ1+jyjMPg8g4shwyyNlRQl6d3L9At02ZHQr5K6s5duZl/+YKMnM3/8pDhoUphg==" crossorigin="anonymous" referrerpolicy="no-referrer" />
 
   <meta name="author" content="{{ site.author }}">
   <meta name="robots" content="{{#if robots}}{{ robots }}{{else}}index, follow{{/if}}">