doc,tools: properly syntax highlight API ref docs

Prior to this commit, all <pre> tags were being
highlighted as JavaScript. This has been corrected
to syntax highlight all languages appearing in the
API reference docs. This was accomplished by using
highlight.js instead of SHJS for the frontend lib.

* remove SHJS JavaScript code
* add highlight.js bundle
* fix script tags to reflect replacement
* migrate CSS to use highlight.js classes
* add appropriate documentation
* ensure api_assets README.md stays interal

Fixes: #33363

PR-URL: #33442
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Ujjwal Sharma <ryzokuken@disroot.org>

LICENSE

@@ -1471,6 +1471,39 @@ The externally maintained libraries used by Node.js are:
      THE POSSIBILITY OF SUCH DAMAGE.
   """
 
+- highlight.js, located at doc/api_assets/highlight.pack.js, is licensed as follows:
+  """
+    BSD 3-Clause License
+
+    Copyright (c) 2006, Ivan Sagalaev.
+    All rights reserved.
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright notice, this
+      list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above copyright notice,
+      this list of conditions and the following disclaimer in the documentation
+      and/or other materials provided with the distribution.
+
+    * Neither the name of the copyright holder nor the names of its
+      contributors may be used to endorse or promote products derived from
+      this software without specific prior written permission.
+
+    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+    DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+    SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+    OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+  """
+
 - node-heapdump, located at src/heap_utils.cc, is licensed as follows:
   """
     ISC License

Makefile

@@ -733,7 +733,7 @@ out/doc/api/assets:
 
 # If it's not a source tarball, we need to copy assets from doc/api_assets
 out/doc/api/assets/%: doc/api_assets/% out/doc/api/assets
-	@cp $< $@
+	@cp $< $@ ; $(RM) out/doc/api/assets/README.md
 
 
 run-npm-ci = $(PWD)/$(NPM) ci

doc/api_assets/README.md

@@ -0,0 +1,27 @@
+# API Reference Document Assets
+
+## highlight.pack.js
+
+_Generated by [highlightjs.org/download][] on 2020-05-16._
+
+Grammars included in the custom bundle:
+
+* Bash
+* C
+* C++
+* CoffeeScript
+* JavaScript
+* JSON
+* Markdown
+* Plaintext
+* Shell Session
+
+## hljs.css
+
+The syntax theme for code snippets in API reference documents.
+
+## style.css
+
+The main stylesheet for API reference documents.
+
+[highlightjs.org/download]: https://highlightjs.org/download/

doc/api_assets/hljs.css

@@ -0,0 +1,29 @@
+.hljs {
+  font-weight: normal;
+  font-style: normal;
+}
+
+.hljs-symbol {
+  color: #333;
+}
+
+.hljs-keyword {
+  color: #338;
+}
+
+.hljs-string,
+.hljs-regexp,
+.hljs-number {
+  color: #E54305;
+}
+
+.hljs-doctag {
+  color: #040404;
+}
+
+.hljs-doctag .hljs-type,
+.hljs-doctag .hljs-variable,
+.hljs-comment {
+  color: #666;
+  font-weight: lighter;
+}