RFR: 8343804: Show the default time zone with -XshowSettings option

[Naoto Sato]

A small enhancement in the Java launcher. For diagnostic purposes, display the default time zone ID with the `-XshowSettings` option.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/21965/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21965&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343804
  Stats: 9 lines in 2 files changed: 7 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21965.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21965/head:pull/21965

PR: https://git.openjdk.org/jdk/pull/21965