git: openjdk/jdk21u: master: 8372534: Update Libpng to 1.6.51

[Andrew John Hughes]

Changeset: 5c2ab8e0
Branch: master
Author:    Andrew John Hughes <andrew at openjdk.org>
Date:      2025-12-18 13:10:33 +0000
URL:       https://git.openjdk.org/jdk21u/commit/5c2ab8e057ccc77019047f9e7e5c4928f876b555

8372534: Update Libpng to 1.6.51

Reviewed-by: mbaesken, sgehwolf
Backport-of: cb7fb728d4805ed4e9d62ce31cee7c948f3d5746

! make/modules/java.desktop/lib/Awt2dLibraries.gmk
! src/java.desktop/share/legal/libpng.md
! src/java.desktop/share/native/libsplashscreen/libpng/CHANGES
! src/java.desktop/share/native/libsplashscreen/libpng/README
! src/java.desktop/share/native/libsplashscreen/libpng/png.c
! src/java.desktop/share/native/libsplashscreen/libpng/png.h
! src/java.desktop/share/native/libsplashscreen/libpng/pngconf.h
! src/java.desktop/share/native/libsplashscreen/libpng/pngdebug.h
! src/java.desktop/share/native/libsplashscreen/libpng/pngerror.c
! src/java.desktop/share/native/libsplashscreen/libpng/pngget.c
! src/java.desktop/share/native/libsplashscreen/libpng/pnginfo.h
! src/java.desktop/share/native/libsplashscreen/libpng/pnglibconf.h
! src/java.desktop/share/native/libsplashscreen/libpng/pngmem.c
! src/java.desktop/share/native/libsplashscreen/libpng/pngpread.c
! src/java.desktop/share/native/libsplashscreen/libpng/pngpriv.h
! src/java.desktop/share/native/libsplashscreen/libpng/pngread.c
! src/java.desktop/share/native/libsplashscreen/libpng/pngrio.c
! src/java.desktop/share/native/libsplashscreen/libpng/pngrtran.c
! src/java.desktop/share/native/libsplashscreen/libpng/pngrutil.c
! src/java.desktop/share/native/libsplashscreen/libpng/pngset.c
! src/java.desktop/share/native/libsplashscreen/libpng/pngstruct.h