Previously, only the permissions for the scripts in bin/ were set. The
permissions for the files in lib/ were not explicity set, leaving them
with the same permissions as the source files in Gradle's cache. This
has proven to be a little brittle when building in certain
environments, leading to test failures. It also assumes that the
file permissions in Gradle's cache will be appropriate for entries in
a distribution archive. That may not always be a reasonable assumption
to make.

To avoid the above-described problems, this commit updates the copy
spec that's used to add files to lib/ in the archive so that each
file uses 0644 for its permissions.

Closes gh-14158