RFR: JDK-8323706 Move SimpleSelector and CompoundSelector to internal packages

[Andy Goryachev]

On Sun, 14 Jan 2024 14:54:36 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

> Moves `SimpleSelector` and `CompoundSelector` to internal packages.
> 
> This can be done with only a minor API break, as `SimpleSelector` and `CompoundSelector` were public before.  However, these classes could not be constructed by 3rd parties.  The only way to access them was by doing a cast (generally they're accessed via `Selector` not by their sub types).  The reason they were public at all was because the CSS engine needs to be able to access them from internal packages.
> 
> This change fixes a mistake (or possibly something that couldn't be modelled at the time) when the CSS API was first made public. The intention was always to have a `Selector` interface/abstract class, with private implementations (`SimpleSelector` and `CompoundSelector`).
> 
> This PR as said has a small API break.  The other changes are (AFAICS) source and binary compatible:
> 
> - Made `Selector` `sealed` only permitting `SimpleSelector` and `CompoundSelector` -- as `Selector` had a package private constructor, there are no concerns with pre-existing subclasses
> - `Selector` has a few more methods that are now `protected` -- given that the class is now sealed, these modified methods are not accessible (they may still require rudimentary documentation I suppose)
> - `Selector` now has a `public` default constructor -- as the class is sealed, it is inaccessible
> - `SimpleSelector` and `CompoundSelector` have a few more `public` methods, but they're internal now, so it is irrelevant
> - `createMatch` was implemented directly in `Selector` to avoid having to expose package private fields in `Match` for use by `CompoundSelector`
> - No need anymore for the `SimpleSelectorShim`

Maybe @jperedadnr could check whether the ScenicView tools uses either SimpleSelector or CompoundSelector?

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PR Comment: https://git.openjdk.org/jfx/pull/1333#issuecomment-1899451079