This commit upgrades to a major new release of HtmlUnit. This is a
breaking change as HtmlUnit 3 moves to a `org.htmlunit` package and
calling code needs to be restructured.
Our use of Selenium has been adapted accordingly, moving to Selenium
3, using the new org.seleniumhq.selenium:htmlunit3-driver integration.
Closes gh-30392
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
Juergen Hoeller
Stéphane Nicoll
anil.senocak
Simon Baslé
Rob Winch