RFR: 7903187: jextract should support --version option

[Athijegannathan Sundararajan]

added --version option that prints the underlying Java version and exits.

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Commit messages:
 - 7903187: jextract should support --version option

Changes: https://git.openjdk.java.net/jextract/pull/31/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jextract&pr=31&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903187
  Stats: 14 lines in 3 files changed: 13 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jextract/pull/31.diff
  Fetch: git fetch https://git.openjdk.java.net/jextract pull/31/head:pull/31

PR: https://git.openjdk.java.net/jextract/pull/31