RFR: 8290844: Add Skin.install() method [v9]

[Jeanette Winzenburg]

On Tue, 4 Oct 2022 19:24:56 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> I don't think we would want to go out of our way to enable this, so I prefer the tighter definition of the life-cycle that Andy is proposing. It seems better to have the Control always call `dispose` and `install` rather than provide an option where the application would call it.
>
> I agree with @kevinrushforth , it's one of the cases when the method is public, but it should not be called by an application, only by its Control.
> 
> Perhaps we should further clarify this fact?

Control is _our_ specific implementation - others might differ :) And not talking about application code but a possibly complete skinnable/skin controlling scheme. 

But I see your point - how can we clearly express that the complete dispose-install cycle should be in the hands of exactly one collaborator (whether a skinnable's property or somewhere else)?

The concrete cells have public methods that are marked as "expert api" - maybe we could do something similar here?

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PR: https://git.openjdk.org/jfx/pull/845