Symfony version(s) affected: 5.0

Description
While documenting the new String component in symfony/symfony-docs#12440 I found something which doesn't make sense to me.

A "grapheme cluster" is a series of one or more code points.

Then, why does our "grapheme string" return a single code point (the first one) instead of all of them for a given cluster?

How to reproduce
Take for example the Hindi word "hello", which is नमस्ते.

$bString = b('नमस्ते');

echo "Bytes: ";
for ($i = 0; $i < $bString->length(); $i++) {
    echo $bString->byteCode($i)." ";
}

$cString = $bString->toCodePointString();
echo "Code Points: ";
for ($i = 0; $i < $cString->length(); $i++) {
    echo $cString->codePoint($i)." ";
}

$uString = $bString->toUnicodeString();
echo "Grapheme Code Points: ";
for ($i = 0; $i < $uString->length(); $i++) {
    echo $uString->codePoint($i)." ";
}

The output is:

Bytes: 224 164 168 224 164 174 224 164 184 224 165 141 224 164 164 224 165 135

Code Points: 2344 2350 2360 2381 2340 2375

Grapheme Code Points: 2344 2350 2360 2340

However, I expected the output to be:

// ...

Grapheme Code Points: 2344 2350 [2360, 2381] [2340, 2375]

Possible Solution
UnicodeString should not return ?int but ?array (the other classes should keep returning ?int).