Add numlines to highlighter

[philipwindecker]

The default highlighter.js solution supported in Antora does not support line numbers. Since these are required by ASAM, an additional script needs to be added to the Antora UI.

Example repo: https://github.com/wcoder/highlightjs-line-numbers.js/

Background

Source highlighting in Antora does not allow linenums.

Reason

Antora, by default, only supports highlighter.js. highlighter.js, in turn, does not support linenums because of design decisions.

Sources

• https://docs.antora.org/antora/2.3/asciidoc/source/
• https://highlightjs.readthedocs.io/en/latest/line-numbers.html

Options

• Remove line number requirement for Antora documents
• Add different highlighter library to Antora UI
• Create custom highlighter.js library with included linenums
• Create extension that pre- or post-processes code content

[philipwindecker]

This relates to #154