tools: fix header escaping regression

quick fix for #22065

Preferred long term fix can be found at:
#22140

PR-URL: #22084
Fixes: #22065
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

tools/doc/generate.js

@@ -67,9 +67,9 @@ fs.readFile(filename, 'utf8', (er, input) => {
 
   const content = unified()
     .use(markdown)
+    .use(html.preprocessText)
     .use(json.jsonAPI, { filename })
     .use(html.firstHeader)
-    .use(html.preprocessText)
     .use(html.preprocessElements, { filename })
     .use(html.buildToc, { filename })
     .use(remark2rehype, { allowDangerousHTML: true })

tools/doc/html.js

@@ -198,7 +198,10 @@ function preprocessElements({ filename }) {
           heading.children = [{
             type: 'text',
             value: file.contents.slice(
-              position.start.offset, position.end.offset),
+              position.start.offset, position.end.offset)
+              .replace('&lt;', '<')
+              .replace('&gt;', '>')
+              .replace(/\\(.{1})/g, '$1'),
             position
           }];
         }