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: https://github.com/nodejs/node/issues/33363

PR-URL: https://github.com/nodejs/node/pull/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>