Verify Pattern, step 2: Integrate behavior change for Pattern.split().

This is the second attempt to submit this CL. The first attempt broke
TextUtilsTest which is now updated by another CL in this topic; also,
the original CL changed behavior for all apps whereas this CL only
changes it for apps targeting API > 28.

This CL integrates a behavior change that was forgotten in the update
from OpenJDK 7u40 to 8u121-b13.

This CL also adds a test to guard against regressions.

Bug: 109659282
Test: testMatchBeginningOfInputSequence() fails before this CL, but
      passes after this CL.
Test: cts-tradefed run singleCommand cts -a arm64-v8a -m CtsLibcoreTestCases \
      -t org.apache.harmony.tests.java.util.regex.SplitTest
Test: cts-tradefed run singleCommand cts -a arm64-v8a -m CtsLibcoreTestCases \
      -t org.apache.harmony.regex.tests.java.util.regex.PatternTest

Change-Id: Ic3631667de0b5cbc4531d42b342d752a701e822f