RFR: Merge openjdk/jdk21u:master

[William Kemper]

Merges tag jdk-21.0.10+6

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Commit messages:
 - 8317970: Bump target macosx-x64 version to 11.00.00
 - 8372534: Update Libpng to 1.6.51

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

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/231/files
  Stats: 660 lines in 23 files changed: 297 ins; 224 del; 139 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/231.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/231/head:pull/231

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/231