Add Verilog syntax highlighting to Antora

[esynr3z]

Antora uses highlight.js for syntax highlighting, but only specific languages are supported:

Syntax highlighting also requires a contribution from the UI. The reference Antora UI bundles the highlight.js library (both the JavaScript and the CSS) and adds it to each page. The names of the languages that are currently supported are listed in the highlight.bundle.js file in Antora’s UI repository.

https://docs.antora.org/antora/latest/asciidoc/source/#source-highlighter

It looks like custom UI bundle need to be created.