RFR: 8338695: GenShen: Clean up jtreg tests

[William Kemper]

Inexplicable merge conflict in SupplementaryLocaleDataProvider.java. Took what was already in the 21 repo, we've never touched that file.

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Commit messages:
 - Fix trailing whitespace
 - Merge remote-tracking branch 'shenandoah-jdk21u/master' into backport-49994b3f
 - 8338695: GenShen: Clean up jtreg tests

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/93/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=93&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338695
  Stats: 496 lines in 16 files changed: 128 ins; 196 del; 172 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/93.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/93/head:pull/93

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/93