RFR: 8285743: Ensure each IntegerPolynomial object is only created once [v2]

[Anthony Scarpino]

On Fri, 29 Apr 2022 22:57:20 GMT, Weijun Wang <weijun at openjdk.org> wrote:

>> All `IntegerPolynimial`s are singletons now. Also, hand-coded implementations for Ed25519 and Ed448 are removed. They were not used since `FieldGen` starts generating classes for them.
>> 
>> No new regression test. This is a clean-up.
>
> Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   move singleton back into impl and make constructor private

I'm good with this change

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Marked as reviewed by ascarpino (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/8476