RFR: JDK-8302323 Add repeat methods to StringBuilder/StringBuffer [v9]

[Jim Laskey]

> Add the ability to repeatedly append char and CharSequence data to StringBuilder/StringBuffer.

Jim Laskey has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 13 additional commits since the last revision:

 - Merge branch 'master' into 8302323
 - Expand test for StringBuffer and illegal code points
 - Add snippet
 - Support code points
 - Move @since in subclasses
 - Move @since
 - Remove @throws IndexOutOfBoundsException
 - Change error report to use "is negative"
 - Optimize for empty CharSequence
 - PR Cleanup
 - ... and 3 more: https://git.openjdk.org/jdk/compare/e62798ac...54a34cf8

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/12728/files
  - new: https://git.openjdk.org/jdk/pull/12728/files/1a77988b..54a34cf8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12728&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12728&range=07-08

  Stats: 379977 lines in 3074 files changed: 221471 ins; 125619 del; 32887 mod
  Patch: https://git.openjdk.org/jdk/pull/12728.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12728/head:pull/12728

PR: https://git.openjdk.org/jdk/pull/12728