RFR: 8302818: Optimize wrapper sets and immutable sets of Enums [v5]

[Tingjun Yuan]

On Tue, 21 Feb 2023 03:39:46 GMT, Tingjun Yuan <duke at openjdk.org> wrote:

>> Currently, the two subclasses of `java.util.EnumSet` optimize bulk operations when the argument is also a `EnumSet`, but there is no such optimization for wrapper sets (returned by `Collections.unmodifiableSet`, `Collections.synchronizedSet`, etc.) and immutable sets (returned by `Set.of` methods) of `Enum`s.
>> 
>> This PR introduces optimization classes for these situations.  No public APIs are changed.
>
> Tingjun Yuan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Set.copyOf: need defensive copy

I have deleted `{Regular,Jumbo}EnumSetCompatible` interfaces and introduced some package-private methods in `AbstractCollection`. This avoids rarely-used checks from static factories in `Collections` and does not reduce much performance compared against the previous implementation.

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PR Comment: https://git.openjdk.org/jdk/pull/12498#issuecomment-1478790594