[php-src] Issue #8475: DateTimeImmutable->diff fails to understand months in Europe/Paris timezone

Issue: https://github.com/php/php-src/issues/8475 Comment Author: hormus DateTime::__construct or DateTimeImmutable::__construct accepts an optional signed integer string if preceded by the @ character. Unix time Stamp through format('U') in php code can be negative for operating systems limited to 32 bits This premise is about how DateTime works, while calculating the difference between two dates is not always reversible. Currently the DateTime class keeps the date object, timezone used is the type while diff from php 8.1.0 if they don't have the same timezone it converts it to UTC. In this scenario it is always wrong as users might interact with different transition periods or even with different timezones than the initial one. A range between two dates should be used for the same transition period and timezone on both sides and for the same version of php. @cmb69 Documentation for DateTime::diff or DateTimeImmutable::diff is missing, accuracy may be inaccurate. Before php 8.1.0 instead of calculating the actual time the constructor erroneously calculated the conversion to UTC which means addition or subtraction offset of the timezone.