Merge "Upgrade libpng to v1.6.40" am: 27bd9cf3d0 am: 6f2b0d3a5f am: edfff8897e am: b936c177bb am: af839e6640

Original change: https://android-review.googlesource.com/c/platform/external/libpng/+/2636112

Change-Id: I0f19b4ac51bb646a1a1d52f3ddd3851e51f93b99
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>