RFR: 8329761: Remove unused KeyBuilder and unusedSets from StyleContext

[Sergey Bylokhov]

On Fri, 5 Apr 2024 15:46:06 GMT, Alexey Ivanov <aivanov at openjdk.org> wrote:

> Remove unused class `KeyBuilder` and unused field `unusedSets`.  
> Update a comment which used javadoc syntax.  
> Mark `KeyEnumeration` and `FontKey` classes as *`final`*.
> 
> All the client tests are green.

Could you please check the history of that file, is these unused due to some functionality was deleted and this was missed, or we planned to implement something and forgot?

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PR Comment: https://git.openjdk.org/jdk/pull/18659#issuecomment-2040218603