[JENKINS-72181] Restore flushed output for 'groovy' CLI command

[daniel-beck]

See JENKINS-72181. Amends #7056.

I accidentally wrapped the PrintWriter in the logging ScriptListener.ListenerWriter that only implements the basic #write(…) and doesn't automatically flush. This switches the order around, so the autoflush in PrintWriter#newLine happens as before.

Testing done

$ echo 'println "Hello"'  | java -jar jenkins-cli.jar -s http://localhost:8080/jenkins/ groovy =
Hello

The added test passes with change in core/src/main/ and fails without.

Proposed changelog entries

• Restore printing output from println and similar methods for the 'groovy' CLI command. (regression in 2.427)

Proposed upgrade guidelines

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[NotMyFault]

/label ready-for-merge

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