Assigning 64bit struct-types to pointers and vice-versa should err

[mhasel]

Describe the bug Currently, assigning any type with an underlying struct-type with a size of exactly 64 bits does not err when assigning the value to a pointer or the other way around. I don't think this is intended/should stay like this

Expected behavior Array and string types are properly validated, even if they are 8 bytes in size. We should do the same for structs.

Tests I've added a failing test in the linked development-branch