Evaluate cross module linkage

As per mail discussion, it would be great if we somehow could get cross module linkage instead of external linkage. One sample is the guide that has links to the Vulkan samples. But that links point to the github repository instead of the Antora module. So when you click such a link from the docs site you jump to github instead of the samples Antora module. Same for the spec/registry links.

Review the guide links to the Vulkan samples and the spec/registry links in the integrated Antora documentation site. Determine how cross-module links are represented, then verify that those links open the corresponding Antora modules instead of the GitHub repository.

Written by the indexing model from the issue text.