OpenJDK 11: Merging in java.lang.String (fix split() fast path)

This CL fixes fast path logic for String#split() method by also
ignoring surrogate characters; and adds a unit test.

Bug: 204795308
Bug: 202962059
Test: atest CtsLibcoreOjTestCases:test.java.lang.String.CompactString.Split
            CtsLibcoreOjTestCases:test.java.lang.String.Split
Change-Id: I54219d1d28c27398576f6c2513628cdcbfbba0ea
3 files changed