Fix const bool subtraction from mixed

[staabm]

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[ondrejmirtes]

This logic is wrong. For example if subtracted type is bool, this condition will pass and toBoolean will return true.

Also many things cast to true or false, making this also wrong.

Here you need something more like if ($this->subtractedType->toBoolean()->isFalse()->yes()).

[staabm]

great catch!

[staabm]

suprisingly its more complicated then initially expected. I think its in better shape now.

[ondrejmirtes]

I still feel this logic is wrong.

1. Let's say we subtract more than what's just falsy. Falsy is 0|0.0|''|'0'|array{}|false|null. But if we subtract more than that, like int|0.0|''|'0'|array{}|false|null or 0|0.0|''|'0'|array{}|bool|null, the result should still be the same.
2. (new ConstantBooleanType(false))->isSuperTypeOf($this->subtractedType)->yes() is also wrong. This represents mixed~false. But something from mixed could still be falsy.

[staabm]

after more iterations, I think it turns out I am chasing ghosts and there is no bug.

the tests I came up with now don't fail any longer before this PR.
you may decide whether the tests are worth merging or we just close here, I guess?

[staabm]

seems the substraction logic atm cannot deal with "subtract more then falsy", as the type stays mixed.
(I think its a different unrelated bug)

[ondrejmirtes]

Thank you!