RFR: 8377526: Update Libpng to 1.6.55

[Jayathirth D V]

Upgrade libpng used for Splashscreen from 1.6.54 to 1.6.55 version.
Testing is green with this update.

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Commit messages:
 - 8377526: Update Libpng to 1.6.55

Changes: https://git.openjdk.org/jdk/pull/29922/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29922&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377526
  Stats: 32 lines in 8 files changed: 7 ins; 0 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/29922.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29922/head:pull/29922

PR: https://git.openjdk.org/jdk/pull/29922