Support ConstantArrayType callables with union values

[herndlm]

Closes phpstan/phpstan#2343

I basically just transformed findTypeAndMethodName(): ?ConstantArrayTypeAndMethod to findTypeAndMethodNames(): ConstantArrayTypeAndMethod[].

[herndlm]

not sure what the best approach here is. I wanted to play it safe and don't touch it at all. But findTypeAndMethodNames is basically a super set of this one. What I want to say - this most likely could be replaced by smth like

/** @deprecated Use findTypeAndMethodNames() instead  */
public function findTypeAndMethodName(): ?ConstantArrayTypeAndMethod
{
    $typeAndMethodNames = $this->findTypeAndMethodNames();
    return count($typeAndMethodNames) === 1 ? $typeAndMethodNames[0] : null;
}

Fyi inside of phpstan it is unused already.

[ondrejmirtes]

This is really nice, thank you! :)