Static analyse if date_create_from_format will fail or not

[pascalheidmann]

Both date_create_from_format and its immutable cousin date_create_immutable_from_format can return DateTime/DateTimeImmutable objects or false on error.

In situations where both $format and $datetime parameters are known (static strings) we can check for results via phpstan and therefore prevent both unnecessary checks during runtime and false positives in phpstan (baseline).

As DateTime::createFromFormat() and DateTimeImmutable::createFromFormat() are both aliases for these functions they are covered as well. OOP variants should work but seem not to do...

[ondrejmirtes]

Thank you!