RFR: Merge openjdk/jdk21u:master

[William Kemper]

Merges tag jdk-21.0.11+2

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Commit messages:
 - 8346048: test/lib/containers/docker/DockerRunOptions.java uses addJavaOpts() from ctor
 - 8356107: [java.lang] Use @requires tag instead of exiting based on os.name or separatorChar property
 - 8354219: Automate javax/swing/JComboBox/ComboPopupBug.java
 - 8355278: Improve debuggability of com/sun/jndi/ldap/LdapPoolTimeoutTest.java test
 - 8345578: New test in JDK-8343622 fails with a promoted build
 - 8372348: Adjust some UL / JFR string deduplication output messages
 - 8330016: Stress seed should be initialized for runtime stub compilation
 - 8375063: Update Libpng to 1.6.54
 - 8375549: ConcurrentModificationException if jdk.crypto.disabledAlgorithms has multiple entries with known oid
 - 8351639: Improve debuggability of test/langtools/jdk/jshell/JdiHangingListenExecutionControlTest.java test
 - ... and 94 more: https://git.openjdk.org/shenandoah-jdk21u/compare/2e594b6c...1cda280a

The webrev contains the conflicts with master:
 - merge conflicts: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=234&range=00.conflicts

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/234/files
  Stats: 14899 lines in 361 files changed: 7757 ins; 4063 del; 3079 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/234.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/234/head:pull/234

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/234