markup/asciidocext: Improve Asciidoctor integration

markup/asciidocext: Improve Asciidoctor integration

Fixes an issue where improper attribute derivation from the page's
relative permalink caused failures with `outdir`, `imagesoutdir`, and
`imagesdir` when `markup.asciidocext.workingFolderCurrent` is enabled.
The updated logic now correctly handles:

- Multi-byte characters
- Multilingual multi-host sites
- Site builds from a subdirectory
- Pages using ugly URLs

Supports diagram caching as implemented in v3.1.0 of the asciidoctor-diagram
extension:

- Enables caching by default
- Sets default cache location to the compiled value of caches.misc.dir

Reduces duration of integration tests by:

- Generating GoAT diagrams instead of Ditaa diagrams
- Taking advantage of asciidoctor-diagram caching

Closes #9202
Closes #10183
Closes #10473
Closes #14160