Unify duplicate copies of harmony {Matcher2,Mode,Replace,Split}Test.

Android is carrying near-duplicate copies of these tests introduced in:
 1.) luni/: commit fdb27044
     (2008-10-21, "Initial Contribution")
 2.) harmony-tests/: commit bfd68b1d
     (2013-05-03, "Add the harmony regex tests.")

The initial copies already differed, eg.

This CL integrates differences between the two copies. After this CL,
the files are pairwise identical except:
 - they are in different packages
 - luni's SplitTest.java is missing the file header

Most of the changes are integrated luni/ -> harmony-tests, keeping
tests that were previously only present in one copy, eg.:

 - slightly more verbose test case in ReplaceTest.testSimpleReplace()
 - SplitTest.testEmptySplits() (added in commit
   51809b9c )
 - Matcher2Test tests added by http://r.android.com/695546

In cases where the "better" version is not clear, an arbitrary judgement
call was made. Examples:

 - @SuppressWarnings("nls"): Differed in the original imports.
   Might be Eclipse specific, but kept for now.
 - minor whitespace changes
 - formatting of ReplaceTest

This CL does not touch the following files / differences:

 - luni/ has PatternTest but harmony-tests/ has MatcherTest
 - luni/ has PatternSyntaxExceptionTest but harmony-tests/ has
   PatternErrorTest

Bug: 109727025
Test: Treehugger
Test: Ran CtsLibcoreTestCases at a later CL.
Change-Id: Ib1c1c25c2010c082e119a0b8b21dadf58576e3f7