RFR: Merge openjdk/jdk21u:master

[William Kemper]

Merges tag jdk-21.0.11+1

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Commit messages:
 - 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
 - 8075917: The regression-swing case failed as the text on label is not painted red with the GTK L&F
 - ... and 93 more: https://git.openjdk.org/shenandoah-jdk21u/compare/2e594b6c...2ce50303

The webrev contains the conflicts with master:
 - merge conflicts: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=233&range=00.conflicts

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/233/files
  Stats: 14895 lines in 361 files changed: 7757 ins; 4063 del; 3075 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/233.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/233/head:pull/233

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/233