RFR: 8289389: Fix warnings: type should also implement hashCode() since it overrides Object.equals() [v5]

[Andy Goryachev]

On Fri, 22 Jul 2022 17:05:06 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> - added missing hashCode() methods
>
> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8289389: review comments

If there are no objections, I'd like to integrate this PR on Monday (25 July)

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PR: https://git.openjdk.org/jfx/pull/821