RFR: JDK-8295685: Update Libpng to 1.6.38 [v4]

[Alexander Zvegintsev]

On Wed, 2 Nov 2022 23:24:18 GMT, Harshitha Onkar <honkar at openjdk.org> wrote:

>> Updated libpng library to v1.6.38.
>> 
>> Following files have been updated -
>> 
>> - 12 source code files of libpng 
>> - LICENSE, README, CHANGES, UPDATING text files
>> - legal/libpng.md
>
> Harshitha Onkar has updated the pull request incrementally with one additional commit since the last revision:
> 
>   consolidated script to remove trailing whitespaces and fix line endings

src/java.desktop/share/native/libsplashscreen/libpng/UPDATING.txt line 9:

> 7: The updated info comes from the LICENSE, TRADEMARK and AUTHORS files.
> 8: 
> 9: 2) Copy LICENSE, README, and CHANGES from the new version into OpenJDK's

I am not sure, but probably we might want also copy TRADEMARK and AUTHORS, since we started to pull info from them to `libpng.md`

src/java.desktop/share/native/libsplashscreen/libpng/UPDATING.txt line 38:

> 36: 5) Run scripts to expand tabs and remove trailing white space from source files.
> 37: 
> 38: First cd into the libpng folder and run the following scripts.

script without s?

src/java.desktop/share/native/libsplashscreen/libpng/UPDATING.txt line 54:

> 52: 
> 53: Make sure all the updated files have UNIX-STYLE (LF) line endings to avoid
> 54: whitespace errors.

This should be already handled by script above.

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PR: https://git.openjdk.org/jdk/pull/10953