Description:
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Various grapheme functions throw exceptions depending on input values.
This was introduced in PHP 8 beta 4.
It is a big BC break and renders some of the functions hard to use.

The test whether start/length/etc. parameters are within the haystack as well as disallowing searching for an empty string with grapheme_strpos($string, "") was changed. 

The pull request https://github.com/php/php-src/pull/5972 seems harmful as it creates a big difference between grapheme_* and the * or mb_* counterparts.

Something as simple as truncating a string to length 20 now has to be written as
  $truncated = grapheme_strlen($string) > 0 ? grapheme_substr($string, 0, 20) : "";
instead of
  $truncated = grapheme_substr($string, 0, 20)l
which seems unnecessarily complicated and different from substr/mb_substr.

Obvious examples are grapheme_substr, grapheme_strpos but I guess all grapheme_-functions should be reexamined and if they are changed the change should be in line with substr, strpos etc.

Test script:
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grapheme_substr("", 0, 1);


Expected result:
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Either false (like pre-beta4) or empty string "" (like substr and mb_substr)

Actual result:
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Fatal error: Uncaught ValueError: grapheme_substr(): Argument #2 ($start) must be contained in argument #1 ($string)