Safe cast of arrays

[Iakh via Digitalmars-d]

https://dlang.org/spec/function.html#function-safety
Current definition of safety doesn't mention cast of arrays.
E.g this code allowed by DMD

int[] f(void[] a) @safe pure
{
     return cast(int[])a;
}

But same void* to int* cast is forbidden.
So we need some rules for dynamic arrays casting.
e.g allow only cast(void[]) as for pointers was done.

And definition of safety should be changed.