Trying to assign to a dereferenced `RValue` panics during codegen

[mhasel]

Describe the bug When trying to assign to a dereferenced pointer which is an RValue (see example below) we currently do not validate against it and will panic during codegen.

To Reproduce Steps to reproduce the behavior:

FUNCTION_BLOCK foo
VAR
    x: INT;
END_VAR
    (REF(x))^ := 3;
END_FUNCTION_BLOCK

I'm not sure if we should try to fix our codegen to account for such code, similar to *&x = ... in other languages, or validate against this.

An equivalent example in C compiles without problems:

int main()
{
    int a = 5;
    *(&a) = 10;
}