[php-src] Issue #11864: INTL support BCP 47 U extension

Issue: https://github.com/php/php-src/issues/11864 Author: frederikbosch ### Description The following code: ```php <?php var_dump(\Locale::setDefault('en-US')); $locale = \Locale::getDefault(); var_dump($locale); $formatter = new \MessageFormatter($locale, '{0, time, medium}'); $result = $formatter->format([new \DateTime('now')]); var_dump($result); var_dump(\Locale::setDefault('en-US-u-hc-h23')); $locale = \Locale::getDefault(); var_dump($locale); $formatter = new \MessageFormatter($locale, '{0, time, medium}'); $result = $formatter->format([new \DateTime('now')]); var_dump($result); ``` Resulted in this output: ``` bool(true) string(5) "en-US" string(11) "11:54:21 PM" bool(true) string(14) "en-US-u-hc-h23" string(11) "11:54:21 PM" ``` But I expected this output instead: ``` bool(true) string(5) "en-US" string(11) "11:54:21 PM" bool(true) string(14) "en-US-u-hc-h23" string(11) "23:54:21" ``` See also: https://3v4l.org/4udaJ. In [the section on the Unicode BCP 47 U Extension of the Unicode Technical Standard #35](https://www.unicode.org/reports/tr35/#u_Extension) you read that the U extension "provides a mechanism for extending language tags for use in various applications by extension subtags". I have no idea whether PHP supports this already. I guess this also depends on the operating system and the version of the underlying ICU library. The test on my locale computer was executed on Alpine 3.18 with icu-data-full 73.2-r2 installed. ### PHP Version PHP 8.x ### Operating System Ubuntu, Alpine, any