Support narrowing down via in_array with enum cases

[herndlm]

Closes phpstan/phpstan#7176

I was wondering if there is a more generic / better way of fixing this. This one at least is the least invasive one I guess.

[herndlm]

I found the other in_array issues now. Looks like there will be one or two more PRs like this and maybe I could look into refactor this then. And, I guess, there was still something with impossible check hacks for in_array which now feels very related. Maybe it's time to look at that then :)

[ondrejmirtes]

Thank you. in_array needs to be rethought completely, right now it's a buggy mess. It's a hard function to get right.