Synchronise ForkJoinPool port with JSR-166 changes for JDK 19

[WojciechMazur]

JSR-166 had a recent update changing the implementation of ForkJoinPool with a goal of better support for VirtualThreads, it also adds new methods and interfaces, eg.:

• ExecutorService now extends AutoClosable
• java.util.concurrent.Future now defines a new enum type Future.State and methods state(): State, resultNow(): V, exceptionNow(): Throwable
• New protected constructor for ForkJoinPool