RFR: Merge openjdk/jdk21u:master

[William Kemper]

Merges tag jdk-21.0.6+5

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Commit messages:
 - 8343877: Test AsyncClose.java intermittent fails - Socket.getInputStream().read() wasn't preempted
 - 8338344: Test TestPrivilegedMode.java intermittent fails java.lang.NoClassDefFoundError: jdk/test/lib/Platform
 - 8316893: Compile without -fno-delete-null-pointer-checks
 - 8340552: Harden TzdbZoneRulesCompiler against missing zone names
 - 8316907: Fix nonnull-compare warnings
 - 8343884: [s390x]  Disallow OptoScheduling
 - 8333248: VectorGatherMaskFoldingTest.java failed when maximum vector bits is 64
 - 8319678: Several tests from corelibs areas ignore VM flags
 - 8339637: (tz) Update Timezone Data to 2024b
 - 8328619: sun/management/jmxremote/bootstrap/SSLConfigFilePermissionTest.java failed with BindException: Address already in use
 - ... and 7 more: https://git.openjdk.org/shenandoah-jdk21u/compare/4b1365ea...50aa07ef

The merge commit only contains trivial merges, so no merge-specific webrevs have been generated.

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/139/files
  Stats: 1877 lines in 45 files changed: 678 ins; 170 del; 1029 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/139.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/139/head:pull/139

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/139