RFR: Merge openjdk/jdk:master

[William Kemper]

Merges tag jdk-21+21

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Commit messages:
 - Merge tag 'jdk-21+21' into merge-jdk-21-21
 - 8306014: Update javax.net.ssl TLS tests to use SSLContextTemplate or SSLEngineTemplate
 - 8068925: Add @Override in javax.tools classes
 - 8306836: Remove pinned tag for G1 heap regions
 - 8306933: C2: "assert(false) failed: infinite loop" failure
 - 8306042: C2: failed: Missed optimization opportunity in PhaseCCP (adding LShift->Cast->Add notification)
 - 8305092: Improve Thread.sleep(millis, nanos) for sub-millisecond granularity
 - 8307005: Make CardTableBarrierSet::initialize non-virtual
 - 8306997: C2: "malformed control flow" assert due to missing safepoint on backedge with a switch
 - 8307106: Allow concurrent GCs to walk CLDG without ClassLoaderDataGraph_lock
 - ... and 86 more: https://git.openjdk.org/shenandoah/compare/84c36e65...b701c556

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.org/?repo=shenandoah&pr=276&range=00.0
 - openjdk/jdk:master: https://webrevs.openjdk.org/?repo=shenandoah&pr=276&range=00.1

Changes: https://git.openjdk.org/shenandoah/pull/276/files
  Stats: 34672 lines in 716 files changed: 20167 ins; 8751 del; 5754 mod
  Patch: https://git.openjdk.org/shenandoah/pull/276.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/276/head:pull/276

PR: https://git.openjdk.org/shenandoah/pull/276