Support for Antora project structure, to render previews in full

[digi-brain]

Is your feature request related to a problem? Please describe

When we write with Asciidoc but for Antora, the preview doesn't doesn't recognise and render elements that depend upon the Antora project structure. This makes it much more difficult to compose good source files than it would otherwise be, and forces us to build locally often just to check basic things.

Describe the solution you'd like

Provide Antora support; in particular, support the project structure so that the preview will correctly render elements such as:

• includes
• attributes that are defined in the playbook, not just in the page
• xrefs between pages/modules/components

Describe alternatives you've considered

I know of no alternatives, other than to switch to IntelliJ and use the Asciidoc plugin which does support Antora. IntelliJ AsciiDoc Plugin: Antora

Additional context

From the Antora Zulip chat forum:

As the current maintainer of the IntelliJ AsciiDoc plugin and its Antora support: If someone wants to tackle some of the features for the VS Code plugin, I'm happy to guide and discuss how this was implemented for the IntelliJ plugin. Mentioning me on GitHub issues as "@ahus1" usually works well.

[digi-brain]

By the way, love the plugin, would just love it even more with Antora support! Keep up the great work.