RFR: 8304020: Speed up test/jdk/java/util/zip/ZipFile/TestTooManyEntries.java and clarify its purpose [v7]

[Eirik Bjorsnos]

On Mon, 30 Oct 2023 14:28:28 GMT, Lance Andersen <lancea at openjdk.org> wrote:

> Please see comments below

Big thanks for your review Lance! I think I have addressed your concerns now.

> I would suggest a comment to help future developers. I realize there are some earlier bread crumbs but I think this would be beneficial

I added a code comment explaining here, and also replaced the `afterLastCEN` variable with a `sparse` variable, flipping the if statements accordingly. Sparse is the 'normal' in this context, so better to have actual writes in the `else` branch.

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PR Comment: https://git.openjdk.org/jdk/pull/12991#issuecomment-1785506785
PR Review Comment: https://git.openjdk.org/jdk/pull/12991#discussion_r1376441175