Add ForkJoinTask.adaptInterruptible

ForkJoinTask.adaptInterruptible is a new method deferred from CSR
https://bugs.openjdk.java.net/browse/JDK-8246587

/**
 * Returns a new {@code ForkJoinTask} that performs the {@code call}
 * method of the given {@code Callable} as its action, and returns
 * its result upon {@link #join}, translating any checked exceptions
 * encountered into {@code RuntimeException}. Additionally,
 * invocations of {@code cancel} with {@code mayInterruptIfRunning
 * true} will attempt to interrupt the thread performing the task.
 *
 * @param callable the callable action
 * @param <T> the type of the callable's result
 * @return the task
 *
 * @since 15
 */
public static <T> ForkJoinTask<T> adaptInterruptible(Callable<? extends T> callable)

 * <p>By default, method {@link #cancel} ignores its {@code
 * mayInterruptIfRunning} argument, separating task cancellation from
 * the interruption status of threads running tasks. However, the
 * method is overridable to accommodate cases in which running tasks
 * must be cancelled using interrupts. This may arise when adapting
 * Callables that cannot check {@code isCancelled()} task status.
 * Tasks constructed with the {@link #adaptInterruptible} adaptor
 * track and interrupt the running thread upon {@code
 * cancel(true)}. Reliable usage requires awareness of potential
 * consequences: Method bodies should ignore stray interrupts to cope
 * with the inherent possibility that a late interrupt issued by
 * another thread after a given task has completed may (inadvertently)
 * interrupt some future task. Further, interruptible tasks should not
 * in general create subtasks, because an interrupt intended for a
 * given task may be consumed by one of its subtasks, or vice versa.