Verify java.util.stream against OpenJDK 8u121-b13 sources.

Significant changes:
 - Add markers for visibility changes.
 - Remove some more unused imports. We had removed some of these, but
   not all.
 - Revert diff in LongStream introduced because Long.divideUnsigned
   wasn't supported. It is now.
 - Revert diff in visibility of SpinedBuffer.OfPrimite as it's not needed.
 - Revert diffs in Stream javadoc and package-info.java. References to
  methods not ported at the time were removed, but they all exist now.

Bug: 35910877
Test: cts-tradefed run cts-dev -m CtsLibcoreOjTestCases
Test: cts-tradefed run cts-dev -m CtsLibcoreTestCases
Test: make docs
Change-Id: Ic5ada257e1700747901ec51b0ae7d9392964a85a