tools: build all.json by combining generated JSON

Notes:

1) Removed a number of root properties that did not seem relevant:
   source, desc, and introduced_in.  There no longer is a source, and
   the other two are from the first include and do not reflect the
   entire API.

2) As with https://github.com/nodejs/node/issues/20100, the current
   "desc" properties sometimes contained in-page links, other times
   referenced another page, and often did not match the links in the
   original HTML or JSON file. I chose to standardize on external links
   as "desc" values are isolated snippets as opposed to all.html which
   can be viewed as a standalone and self contained document.

3) Eliminated preprocessing for @include entirely, including the test
   case for this function.

4) _toc.md was renamed to index.md.

5) index comments no longer appear in embedded TOCs (left hand side
   column in the generated documentation.

PR-URL: https://github.com/nodejs/node/pull/21637
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

tools/doc/allhtml.js

@@ -12,7 +12,7 @@ const htmlFiles = fs.readdirSync(source, 'utf8')
   .filter((name) => name.includes('.html') && name !== 'all.html');
 
 // Read the table of contents.
-const toc = fs.readFileSync(source + '/_toc.html', 'utf8');
+const toc = fs.readFileSync(source + '/index.html', 'utf8');
 
 // Extract (and concatenate) the toc and apicontent from each document.
 let contents = '';
@@ -47,11 +47,12 @@ for (const link of toc.match(/<a.*?>/g)) {
   seen[href] = true;
 }
 
-// Replace various mentions of _toc with all.
-let all = toc.replace(/_toc\.html/g, 'all.html')
-  .replace('_toc.json', 'all.json')
-  .replace('api-section-_toc', 'api-section-all')
-  .replace('data-id="_toc"', 'data-id="all"');
+// Replace various mentions of index with all.
+let all = toc.replace(/index\.html/g, 'all.html')
+  .replace('<a href="all.html" name="toc">', '<a href="index.html" name="toc">')
+  .replace('index.json', 'all.json')
+  .replace('api-section-index', 'api-section-all')
+  .replace('data-id="index"', 'data-id="all"');
 
 // Clean up the title.
 all = all.replace(/<title>.*?\| /, '<title>');