RFR: JDK-8304959: Public API in javafx.css.Match should not return private API class PseudoClassState [v2]

[John Hendrikx]

On Sat, 8 Apr 2023 20:33:43 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> The class `PseudoClassState` is private API, but was exposed erroneously in the CSS API. Instead, `Set<PseudoClass>` should have been used. This PR corrects this.
>
> John Hendrikx has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Ensure Set PseudoClass and StyleClass are immutable in CSS API
>   
>   Updated documentation, fixed warnings and removed some unnecessary code

I had to pull in some of the fixes I did in `BitSet` in https://github.com/openjdk/jfx/pull/1076

Just wrapping a `Set<PseudoClass>` in an unmodifiable set is enough to break lots of tests, because `BitSet` has many methods that will simply do nothing if the "other" `Set` is not a `BitSet`.

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PR Comment: https://git.openjdk.org/jfx/pull/1070#issuecomment-1500980807