<i18n dev> RFR: 8294008: Graphme implementation of setText() throws IndexOutOfBoundsException

[Naoto Sato]

Fixing JCK failures caused by the new grapheme implementation. The length of a CharSequence should return the `endIndex`, not `endIndex - beginIndex`.

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Commit messages:
 - 8294008: Graphme implementation of setText() throws IndexOutOfBoundsException

Changes: https://git.openjdk.org/jdk/pull/10349/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10349&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294008
  Stats: 6 lines in 2 files changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10349.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10349/head:pull/10349

PR: https://git.openjdk.org/jdk/pull/10349