Migrate old tests and/or write new ones

[alexjpwalker]

As we migrate from Jekyll to Antora (and from Markdown to AsciiDoc) our old tests unilaterally cease to work.

We should verify the following in our correctness workflow in CI:

• Standard Java/Maven correctness checks (artifacts.snapshot, unused deps);
• Test that all TypeQL queries and typeql-lang-* snippets are valid.
• Test that all Java, Python, TypeScript and Rust snippets run.
• Test that there are no dead links in the site.