RFR: 8310813: Simplify and modernize equals, hashCode, and compareTo for BigInteger [v12]

[Raffaello Giulietti]

On Thu, 11 Jan 2024 10:34:45 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>> Please review this PR to use modern APIs and language features to simplify equals, hashCode, and compareTo for BigInteger. If you have any performance concerns, please raise them.
>> 
>> This PR is cherry-picked from a bigger, not-yet-published PR, to test the waters. That latter PR will be published soon.
>
> Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert copyright year change
>   
>   Those files were first published in 2023 and haven't been changed since.

LGTM

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Marked as reviewed by rgiulietti (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14630#pullrequestreview-1815217411