fix(aio): fix window title on Home page (#20440)

Using `display: none` on the `<h1>` causes `innerText` to not work as expected
and include the icon ligature (`link`) in the title. This caused the window
title on the angular.io Home page to appear as "Angular - link".
This commit fixes it by not generating anchors at all for headings with the
`no-anchor` class.

Fixes #20427

PR Close #20440

aio/tools/transforms/angular-base-package/post-processors/autolink-headings.js

@@ -1,9 +1,34 @@
+const has = require('hast-util-has-property');
+const is = require('hast-util-is-element');
 const slug = require('rehype-slug');
-const link = require('rehype-autolink-headings');
+const visit = require('unist-util-visit');
 
 /**
- * Get remark to inject anchors into headings
+ * Get remark to add IDs to headings and inject anchors into them.
+ * This is a stripped-down equivalent of [rehype-autolink-headings](https://github.com/wooorm/rehype-autolink-headings)
+ * that supports ignoring headings with the `no-anchor` class.
  */
+const HEADINGS = ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'];
+const NO_ANCHOR_CLASS = 'no-anchor';
+
+const clone = obj => JSON.parse(JSON.stringify(obj));
+const hasClass = (node, cls) => {
+  const className = node.properties.className;
+  return className && className.includes(cls);
+};
+
+const link = options =>
+  tree => visit(tree, node => {
+    if (is(node, HEADINGS) && has(node, 'id') && !hasClass(node, NO_ANCHOR_CLASS)) {
+      node.children.unshift({
+        type: 'element',
+        tagName: 'a',
+        properties: Object.assign(clone(options.properties), {href: `#${node.properties.id}`}),
+        children: clone(options.content)
+      });
+    }
+  });
+
 module.exports = [
   slug,
   [link, {
@@ -12,11 +37,13 @@ module.exports = [
       className: ['header-link'],
       'aria-hidden': 'true'
     },
-    content: {
-      type: 'element',
-      tagName: 'i',
-      properties: {className: ['material-icons']},
-      children: [{ type: 'text', value: 'link' }]
-    }
+    content: [
+      {
+        type: 'element',
+        tagName: 'i',
+        properties: {className: ['material-icons']},
+        children: [{ type: 'text', value: 'link' }]
+      }
+    ]
   }]
 ];