[JENKINS-74814] java.lang.UnsupportedOperationException: This stack walker does not have RETAIN_CLASS_REFERENCE access

[basil]

See JENKINS-74814. When attempting to use the zero-argument version of jenkins.util.SetContextClassLoader from #6575 in ldap-plugin, I got this exception:

java.lang.UnsupportedOperationException: This stack walker does not have RETAIN_CLASS_REFERENCE access
	at java.base/java.lang.StackWalker.getCallerClass(StackWalker.java:687)
	at jenkins.util.SetContextClassLoader.<init>(SetContextClassLoader.java:65)
	at PluginClassLoader for ldap//hudson.security.LDAPSecurityRealm$LDAPAuthenticationManager.authenticate(LDAPSecurityRealm.java:989)
	at org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter.attemptAuthentication(UsernamePasswordAuthenticationFilter.java:85)
	at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:231)
	at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:221)
	at hudson.security.ChainedServletFilter2$1.doFilter(ChainedServletFilter2.java:99)

This apparently has never worked, but the bug was easy to fix by configuring the stack walker with the StackWalker.Option.RETAIN_CLASS_REFERENCE option (which instructs the stack walker to retain class information in each stack frame).

Testing done

Reproduced the problem in context in a draft ldap-plugin change and verified that after this PR the problem was resolved.

Proposed changelog entries

• Developer: Allow context classloaders to be defined without making explicit reference to the calling class.

Proposed upgrade guidelines

N/A

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[MarkEWaite]

This PR is now ready for merge. We will merge it after approximately 24 hours if there is no negative feedback.

/label ready-for-merge