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

[Mikhail Yankelevich]

On Thu, 24 Jul 2025 14:50:07 GMT, Tatsunori Uchino <duke at openjdk.org> wrote:

> 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?

src/java.base/share/classes/java/lang/Character.java line 9969:

> 9967:         int n = length;
> 9968:         for (int i = 0; i < length; ) {
> 9969:             if (isHighSurrogate(seq.charAt(i++)) && i < length &&

Imo this is quite hard to read, especially with `i++` inside of the if statement. What do you think about changing it to this? 
```java 
for (int i = 0; i < length; i++) {
    if (isHighSurrogate(seq.charAt(i)) && 
         i+1 < length && 
         isLowSurrogate(seq.charAt(i+1))) {

         n--;
         i++;
    }
}

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PR Review Comment: https://git.openjdk.org/jdk/pull/26461#discussion_r2229676944