RFR: 8302818: Optimize wrapper sets and immutable sets of Enums [v2]

[Tingjun Yuan]

On Mon, 20 Feb 2023 13:15:20 GMT, liach <duke at openjdk.org> wrote:

> Bad change, doesn't handle e0.equals(e1), and this is getting beyond the original issue

`Set.of(E, E)` handles duplication. If `coll` is `{Jumbo,Regular}EnumSetCompatible`, then we don't have to create the `HashSet`.

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