[jdk21u-dev] RFR: 8348598: Update Libpng to 1.6.47

[Goetz Lindenmaier]

I backport this for parity with 21.0.8-oracle.

Had to resolve makefile because png make code is in
ClientLibraries.gmk in head but in Awt2dLibraries.gmk in 21.

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Commit messages:
 - Backport 6b82b42a2116900b2125e03c1ffa0824d6062757

Changes: https://git.openjdk.org/jdk21u-dev/pull/1556/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1556&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348598
  Stats: 4890 lines in 20 files changed: 1906 ins; 2195 del; 789 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1556.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1556/head:pull/1556

PR: https://git.openjdk.org/jdk21u-dev/pull/1556