RFR: 8364007: Add no-argument codePointCount method to CharSequence and String [v9]

[Tatsunori Uchino]

> Adds `codePointCount()` overloads to `String`, `Character`, `(Abstract)StringBuilder`, and `StringBuffer` to make it possible to conveniently retrieve the length of a string as code points without extra boundary checks.
> 
> 
> if (superTremendouslyLongExpressionYieldingAString().codePointCount() > limit) {
>     throw new Exception("exceeding length");
> }
> 
> 
> Is a CSR required to this change?

Tatsunori Uchino has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Remove `Character.codePointCount()`

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26461/files
  - new: https://git.openjdk.org/jdk/pull/26461/files/a26398c9..c9719d4e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26461&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26461&range=07-08

  Stats: 26 lines in 3 files changed: 0 ins; 23 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/26461.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26461/head:pull/26461

PR: https://git.openjdk.org/jdk/pull/26461