Use unsealed shapes in conditional return types

[IanDelMar]

Closes #248

[kkmuffme]

That's perfect how it should be in an ideal world :-) Unfortunately, some tools (afair phpstorm for example), still don't support the "..." syntax, but do support the &array syntax.

If you could just Search/Replace All ,... } with }&array ?

[IanDelMar]

I opted for the ,... } to avoid stating that the intersection of {A, B, C} and {C, D, E} is anything other than C. 😞 But will change to }&array...

[IanDelMar]

@szepeviktor This PR is complete.

[szepeviktor]

Unfortunately, some tools (afair phpstorm for example),

Viktor is also afraid.