OpenJDK 11: Merging in java.io.Reader and Writer

This is part of merging upstream changes from OpenJDK 11.28. This CL
merges java.io.Reader and Writer.

There are 2 new APIs added for java.io.Reader:
    static Reader nullReader();
    long transferTo(Writer) throws IOException;

And 1 added for Writer:
    static java.io.Writer nullWriter();

Tests were added for all of the new APIs.

Test: m droid
Test: atest CtsLibcoreTestCases:libcore.java.io.Reader.{TestName}
Test: atest CtsLibcoreTestCases:libcore.java.io.Writer.NullWriter
Change-Id: I11d68d4e01f581465a250527d88ffae489c3a875
6 files changed