RFR: 8364007: Add overload without arguments to codePointCount in String etc. [v3]

[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 updated the pull request incrementally with four additional commits since the last revision:

 - Update `@bug` in correct file
 - Add default implementation on codePointCount in CharSequence
 - Update `@bug` entries in test class doc comments
 - Discard changes on code whose form is not `str.codePointCount(0, str.length())`

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26461/files
  - new: https://git.openjdk.org/jdk/pull/26461/files/63eb4a7d..0e55e35c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26461&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26461&range=01-02

  Stats: 32 lines in 5 files changed: 26 ins; 0 del; 6 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