[jdk21u] RFR: 8316030: Update Libpng to 1.6.40

Thu Nov 9 18:43:58 UTC 2023

On Thu, 9 Nov 2023 00:33:16 GMT, Rajat Mahajan <rmahajan at openjdk.org> wrote:

> 8316030: Update Libpng to 1.6.40

Clean backport. Changes look good. 
You might want to run and check the Splash screen tests to make sure everything looks good with the libpng changes on 21u.

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PR Review: https://git.openjdk.org/jdk21u/pull/341#pullrequestreview-1723267668