[jdk18] RFR: 8278574: update --help-extra message to include default value of --finalization option

[Stuart Marks]

A small modification to the Launcher's help text.

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Commit messages:
 - Update launcher usage message to mention finalization default

Changes: https://git.openjdk.java.net/jdk18/pull/34/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=34&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278574
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/34.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/34/head:pull/34

PR: https://git.openjdk.java.net/jdk18/pull/34