Prior to this commit, Spring Framework would ship several abstract
`*View` implementations for rendering PDF, RSS or XLS documents using
well-known libraries. More recently, supporting libraries evolved a lot
with new versions and forks. Spring Framework is not in a position to
efficiently support all variants within the project.
This commit deprecates the relevant classes. Instead, libraries can
reuse existing code and ship optional support for Spring directly.
Often, updating imports and library usage is enough.
As an alternative, applications can decide to perform rendering
direclty in web handlers.
Closes gh-35451
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
Brian Clozel
Juergen Hoeller
Sam Brannen
Rob Winch