Fix for grapheme bug 61860

Hi! I've started working on fixing bug #61860 (where grapheme case insensitive functions mess up offsets for complex case folding) and ended up rewriting the string search functions to use proper ICU API for that - USearch. All tests seem to be passing just fine, and it is what it should be doing from the start, but I do not completely trust that our tests there are full. So if someone uses grapheme string functions with real code & tests, could you please check out this pull: https://github.com/php/php-src/pull/362 And see if nothing breaks for you and notify me if anything does so I could add it to the tests. If nothing breaks, I'll commit it shortly. -- Stanislav Malyshev, Software Architect SugarCRM: http://www.sugarcrm.com/ (408)454-6900 ext. 227