Add grapheme_mask() function Grapheme mask

[sepehrphpr]

This PR implements the grapheme_mask() function as proposed in the RFC:

https://wiki.php.net/rfc/grapheme_mask

The function works similarly to str_mask() but operates on grapheme cluster

boundaries instead of bytes/code points, making it fully Unicode-safe.

It uses ICU BreakIterator for grapheme boundary detection, consistent with

other grapheme_*() functions in ext/intl.

Changes:

Added grapheme_mask.c and grapheme_mask.h (Modified BSD license)
Implemented grapheme_mask() using ICU BreakIterator
Added grapheme_mask() declaration to grapheme.stub.php
Generated grapheme_arginfo.h
Added grapheme_mask.phpt test case

[youkidearitai]

Please do not change file structure. Your RFC is not include it.

Please only add about intl/grapheme/grapheme.cpp, intl/php_intl.stub.php and *.phpt files. Probably enough them files that this RFC.

[youkidearitai]

And, Please close #22605 if you continue this pull request.