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

[Phil Race]

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

Looks fine on the understanding that you built  + tested on all platforms - running all automated tests.

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Marked as reviewed by prr (Reviewer).

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