Add the ability to repeatedly append char and CharSequence data to StringBuilder/StringBuffer.
------------- Commit messages: - Clean up fro CSR - Add synchronized to StringBuffer repeats - AbstractStringBuilder repeat Changes: https://git.openjdk.org/jdk/pull/12728/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12728&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8302323 Stats: 340 lines in 5 files changed: 336 ins; 0 del; 4 mod Patch: https://git.openjdk.org/jdk/pull/12728.diff Fetch: git fetch https://git.openjdk.org/jdk pull/12728/head:pull/12728 PR: https://git.openjdk.org/jdk/pull/12728
