Updated Constables and constant folding doc

[Brian Goetz]

> the way the constant folding is done in this proposal scare me a lot,

It should scare you, it means you are reading ...

> pre-linking is usually a bad idea when done in the compiler because it means that the world the compiler sees and the world VM sees has to be exactly the same,

Yes, it means that the bar for @Foldable/Constable is very, very high.

> and there is nothing in the spec that guarantee that the compiler and the VM are the same.

It means that the implementation of the @F/C classes must guarantee this.

Because of all the constraints, its use will be limited to java.base.