OpenJDK 11: Merging in java.util.SplittableRandom

This is part of merging upstream changes from OpenJDK 11+28. This CL
updates java.util.SplittableRandom; and merges unit tests for it.

There is a new API added in java.util.SplittableRandom:
 * void nextBytes(byte[] bytes);

The JDK tests testing this API were also merged in.

Test: m droid
Test: atest SplittableRandomTest
Change-Id: Iebe1b4cf2eef2fc14aa50d051646993940b16a7a
3 files changed