[JENKINS-55681] - Make JAXB a detached plugin only on Java 11 (#3865)

* Move detached plugins logic into a dedicated class

ClassicPluginStrategy is already long enough, so trying to make things a
bit more focused before adding Java 11 logic. (and even if not, the change
still splits a class that is almost 1k lines).

* Install jaxb as detached only on Java 11+

* Remove duplicate @Restricted

Given the enclosing class already has it.

* Use 1.5 release

* Add more test coverage

* getMinJavaVersion => getMinimumJavaVersion

* Rename DetachedPluginsManager as DetachedPluginsUtil

as requested by Oleg and Jesse. Mainly because of the misleading
relationship (there's no inheritance) with the existing `PluginManager`
class.

* 🤦

 adjust to 1.5 release method renaming

* Clarify minimum Java version column

Co-Authored-By: batmat <bmathus@gmail.com>

* Update to 2.3.0 version of the jaxb plugin

* Bump minimum core version to next expected release version

* Add preventive cycle breaks for jaxb while waiting for JENKINS-28942

As requested by Oleg.

* Add test to fail fast on wrong format for split-plugins.txt