Bug report

Hi,

When I have a variable of type array{a: string}|array{b: string} (i.e. union of two array shapes, one with key a and one with key b) I would expect that after an if (isset($arr['a'])) check the type is array{a: string} and the impossible type in the union is removed. And I would expect the opposite to happen for remaining branches (i.e.: remove all types which already applied), meaning that if it's followed by an else that the only possible type is array{b: string}. But this isn't the case. While if / elseif properly removes invalid types from the union, it seems like handled types aren't removed for the remainder of the elseif / else cases.

Code snippet that reproduces the problem

https://phpstan.org/r/cdc39146-ba14-4841-85b4-889368a2c09d

Expected output

On line 10 I would expect Dumped type: array{c: string} and on line 18 I would expect Dumped type: *NEVER* (because no values in the union remain)

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