[jdk26u] RFR: 8375063: Update Libpng to 1.6.54

[Jayathirth D V]

8375063: Update Libpng to 1.6.54

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Commit messages:
 - Backport a2e749572e03dd394d123b701e163e3837472dd0

Changes: https://git.openjdk.org/jdk26u/pull/21/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk26u&pr=21&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375063
  Stats: 1406 lines in 16 files changed: 443 ins; 7 del; 956 mod
  Patch: https://git.openjdk.org/jdk26u/pull/21.diff
  Fetch: git fetch https://git.openjdk.org/jdk26u.git pull/21/head:pull/21

PR: https://git.openjdk.org/jdk26u/pull/21