[php-src] Issue #12341: ext/xml case folding broken for non-ASCII characters

Issue: https://github.com/php/php-src/issues/12341 Author: nielsdos ### Description See ext/xml/tests/xml007.phpt The code will never run in 8.2 or up because of changes to how strtoupper works. This means the test will be skipped due to the SKIPIF settings which has a locale-dependent strtoupper check. Removing the SKIPIF shows that the test is indeed broken, even on systems where it worked on 8.1 it won't work on 8.2. Other than that, this never worked properly because it depends on the locale. From https://www.w3.org/TR/WD-xml-970807.xml > case-folding: a process applied to a sequence of characters, in which those identified as > non-uppercase (in scripts which have case distinctions) are replaced by their uppercase equivalents, > as specified in The Unicode Standard, Version 2.0, section 4.1. Note that Unicode recommends folding > to lowercase; for compatibility reasons, XML processors must fold to uppercase. Case-folding, as > described here, neither requires nor forbids the normalization of Unicode character sequences into > canonical form (e.g. as described in The Unicode Standard, section 5.9). So it's not supposed to depend on the locale. ### PHP Version 8.1 / 8.2 depending on your point of view ### Operating System _No response_