RFR: 8297561: Redundant index check in String.offsetByCodePoints() [v2]

[Sergey Tsypanov]

> `String.offsetByCodePoints()` delegates to `Character.offsetByCodePoints()` which in turn specifies the same exception thrown under the same conditions and the implementation does exactly the same checks. This means we can remove the check from `String.offsetByCodePoints()` and rely on the one of `Character.offsetByCodePoints()`.

Sergey Tsypanov 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 three additional commits since the last revision:

 - Merge branch 'master' into JDK-8297561
 - 8297561: Add benchmark
 - 8297561: Redundant index check in String.offsetByCodePoints()

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11350/files
  - new: https://git.openjdk.org/jdk/pull/11350/files/9b844f35..1fdc0197

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11350&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11350&range=00-01

  Stats: 13546 lines in 539 files changed: 9038 ins; 2549 del; 1959 mod
  Patch: https://git.openjdk.org/jdk/pull/11350.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11350/head:pull/11350

PR: https://git.openjdk.org/jdk/pull/11350