RFR: 8350048: Enforce threading restrictions for show and hide methods in Window, Control, and Skin

[Kevin Rushforth]

On Wed, 19 Feb 2025 20:39:19 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> - enforced fx application thread
> - added a headful test `TestThreadingRestrictions`
> 
> ## Note to the Reviewers
> 
> To avoid merge conflicts, the preferred order of integrations:
> 
> #1697 
> #1713 
> #1717

Reviewers: @kevinrushforth @arapte

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PR Comment: https://git.openjdk.org/jfx/pull/1717#issuecomment-2678740549