TextUtils: track behavior change of Pattern.split() when targeting > 28.

Another CL in this topic changes the behavior of String.split() and
Pattern.split() to omit a "" generated by a leading zero-width match.
TextUtils.split() is implemented on top of these methods and therefore
adopts the behavior change by default.

The behavior change only affects apps targeting API versions > 28.

Test: cts-tradefed run singleCommand cts-dev -m CtsTextTestCases \
      -t android.text.cts.TextUtilsTest
Test: cts-tradefed run singleCommand cts-dev -m CtsLibcoreTestCases
Bug: 109659282

Change-Id: I8abe251353f8eacf1429ac9a8e272d50a0944c29