RFR: 8290844: Add Skin.install() method [v4]

[Jeanette Winzenburg]

On Fri, 12 Aug 2022 18:15:37 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> - added Skin.install()
>> - javadoc changes for Skinnable.setSkin(Skin)
>> 
>> no code changes for Skinnable.setSkin(Skin) yet.
>
> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8290844: review comments

hmm .. with the singleton handler problem (f.i. [JDK-8268877](https://bugs.openjdk.org/browse/JDK-8268877)) out off the way (a skin must not set such a handler), it seems we are very near to a solution without a problem: none of our skins would want to really implement install (due to the high risk of breaking existing custom skins). 

Nevertheless, the idea is good and a step into the right direction. But would be a bit weird not implementing it ourselfves .. what about refactor all our skins (move the complete installation into install, including  listeners, children, mutations) and - circling back to the supportsInstall :) - implement the concrete subclasses to self-install in the constructor? All our skins extend from SkinBase, so the method might reside there (could be protected) if Skin should remain skinny ..

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