RFR: JDK-8302323 Add repeat methods to StringBuilder/StringBuffer [v6]

[Jim Laskey]

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

Jim Laskey has updated the pull request incrementally with one additional commit since the last revision:

  Support code points

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12728/files
  - new: https://git.openjdk.org/jdk/pull/12728/files/34c7948c..02a4cc70

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12728&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12728&range=04-05

  Stats: 72 lines in 4 files changed: 46 ins; 12 del; 14 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