RFR: 8291660: Grapheme support in BreakIterator [v3]

[Naoto Sato]

> This is to enhance the character break analysis in `java.text.BreakIterator` to conform to the extended grapheme cluster boundaries defined in https://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries. A corresponding CSR has also been drafted, as there will be behavioral changes with this modification.

Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:

  Reverting the fix to BreakIterator.isBoundary()

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9991/files
  - new: https://git.openjdk.org/jdk/pull/9991/files/a772c3a1..d2608451

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9991&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9991&range=01-02

  Stats: 32 lines in 3 files changed: 19 ins; 6 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/9991.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9991/head:pull/9991

PR: https://git.openjdk.org/jdk/pull/9991