git: openjdk/jdk21u: master: 8316030: Update Libpng to 1.6.40

[Alexey Ivanov]

Changeset: 015dab9a
Author:    Rajat Mahajan <rmahajan at openjdk.org>
Committer: Alexey Ivanov <aivanov at openjdk.org>
Date:      2023-11-15 20:34:14 +0000
URL:       https://git.openjdk.org/jdk21u/commit/015dab9a0a1ae7c5ce5643009d6d396cc4ec52b2

8316030: Update Libpng to 1.6.40

Backport-of: 158293d2517695f8c5eaca1b46ecf0f1f9f09691

! src/java.desktop/share/legal/libpng.md
! src/java.desktop/share/native/libsplashscreen/libpng/CHANGES
! src/java.desktop/share/native/libsplashscreen/libpng/LICENSE
! 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/pngget.c
! src/java.desktop/share/native/libsplashscreen/libpng/pnglibconf.h
! src/java.desktop/share/native/libsplashscreen/libpng/pngpriv.h
! src/java.desktop/share/native/libsplashscreen/libpng/pngset.c