[JENKINS-31932] avoid synchronization for Jenkinsget/setJDKs

IdleOfflineCause changelogs and @since

[FIXES JENKINS-31932]

Documenting IllegalStateException from PosixAPI

create a specific implementation for Idle Offline Cause

Specify --webroot to the Windows service wrapper

Docker images and other automation use cases often want to make Jenkins
use specific port. Today they do this via init.groovy.d with a
problematic sleep timeout, so allow them to control this value via
system property.

[FIX JENKINS-11016] Add button that allows retrying core update

[FIXED JENKINS-31219] A CloudProvisioningListener can prevent provisi…

[FIXED JENKINS-31954] Stack overflow reconfiguring some settings where Descriptor.newInstance is gratuitously overridden.

Ensure that no warnings appear during startup