RFR: samples fixes for JDK 21 panama API changes and version change.

Tue Jul 25 10:21:21 UTC 2023

All samples fine on MacOS. I changed run_windows scripts but I've not tested samples on Windows.

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Commit messages:
 - trailing whitespace
 - samples fixes for JDK 21 panama API changes and version change.

Changes: https://git.openjdk.org/jextract/pull/126/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=126&range=00
  Stats: 224 lines in 30 files changed: 50 ins; 77 del; 97 mod
  Patch: https://git.openjdk.org/jextract/pull/126.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/126/head:pull/126

PR: https://git.openjdk.org/jextract/pull/126