Prior to this commit, some same-page links in our Antora-based docs
were written using the `xref:` macro, which Antora resolves as a
cross-page reference. However, a same-page target can be misread as a
page reference and break the site build (as nearly happened in
gh-37152), whereas `<<id,text>>` only ever resolves against the current
page's own anchors.
To address that inconsistency and avoid potential future bugs (broken
links), this commit converts all such same-page `xref:` links to
`<<id,text>>`, leaving genuine cross-page `xref:` links are unaffected.
Closes gh-37161
This commit extract spring-related links and recurring external links
into asciidoctor attributes to be used by the Antora toolchain.
It notably homogenizes links to:
- IETF RFCs
- Java Community Process JSRs
- the Java API Documentation (on the Java 17 version)
- Kotlin documentations (on the Kotlinlang.org version)
- the Spring Boot reference guide (on the `html` version)
This commit also reworks most link attributes to follow a
Project-Category-Misc syntax. For example, `spring-boot-docs` rather
than `docs-spring-boot`.
Finally, it makes an effort to clean up remainders from the previous
documentation toolchain, namely the `docs/asciidoc` folder and
`modules/ROOT/pages/attributes.adoc` file.
Closes gh-26864
Closes gh-31619
Sam Brannen
Juergen Hoeller
Simon Baslé
Rob Winch