Add dynamic return type extension for mb_substitute_character

[TRowbotham]

No description provided.

[TRowbotham]

What is the best way to fix the failing test in PHP 7.1 since the integer range depends on the PHP version? I could add a third test file, but that seems overkill.

[staabm]

I could add a third test file, but that seems overkill.

kind of agree.

maybe run the data/mb_substitute_character.php only on php 7.2+ and leave php 7.1 alone?

another alternative could be dropping the single assertion \PHPStan\Testing\assertType('\'entity\'|\'long\'|\'none\'|int<0, 1114111>', mb_substitute_character()); for the php 7.x test

[TRowbotham]

I went with skipping the test on PHP 7.1. I tried using an if statement in the test file, but that didn't seem to work.

[ondrejmirtes]

Perfect, thank you!