RFR: 7904073: Derive required symbols from client code to minimize generated bindings

[Nizar Benalla]

Please review this change to add a small sample that extracts full bindings once, scans the compiled client classes to collect actually referenced symbols, filters the includes list, and re-runs jextract to produce a slim binding set.

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Commit messages:
 - add new sample

Changes: https://git.openjdk.org/jextract/pull/288/files
  Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=288&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904073
  Stats: 183 lines in 7 files changed: 182 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jextract/pull/288.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/288/head:pull/288

PR: https://git.openjdk.org/jextract/pull/288