RFR: 8302818: Optimize wrapper sets and immutable sets of Enums

[Tingjun Yuan]

On Thu, 9 Feb 2023 16:20:31 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.

Oops, my bad. Please ignore the merge warning.

I've just add several tests for `Set.of` factories.

By the way, I've just built the JDK successfully on my Mac, and the tests run successfully too. Let me know if it fails on other operating systems.

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PR: https://git.openjdk.org/jdk/pull/12498