RFR: 8329342: GenShen: Synchronize shenandoah-jdk21u:master with shenandoah:master

[William Kemper]

Pull in recent changes from shenandoah:master, _en masse_.

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Commit messages:
 - Sync up gtest test
 - Merge remote-tracking branch 'shenandoah-21/master' into synch-up-with-shenandoah-master
 - Fix up tests
 - Sync up with shenandoah tip
 - Merge remote-tracking branch 'openjdk-21u-dev/master' into synch-up-with-shenandoah-master
 - 8328825: Google CAInterop test failures
 - 8328948: GHA: Restoring sysroot from cache skips the build after JDK-8326960
 - 8327261: Parsing test for Double/Float succeeds w/o testing all bad cases
 - 8319648: java/lang/SecurityManager tests ignore vm flags
 - 8326948: Force English locale for timeout formatting
 - ... and 115 more: https://git.openjdk.org/shenandoah-jdk21u/compare/2531dfa3...6e465522

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/29/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=29&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329342
  Stats: 27289 lines in 545 files changed: 14653 ins; 7206 del; 5430 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/29.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/29/head:pull/29

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/29