This commit fixes syntax errors in Java, Kotlin, and XML examples in
the reference manual, such as Java syntax in Kotlin examples,
unbalanced braces and parentheses, and unclosed XML elements.
Closes gh-37392
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
Since we now use asciidoctor-tabs instead of spring-asciidoctor-backends,
we no longer need the `role="primary"` and `role="secondary"` attributes
for tab groups.
Closes gh-33506
Sam Brannen
Juergen Hoeller
Tony Wen
Rob Winch