// data starts at p, with length and capacity equal to n.
//
// This is like [unsafe.Slice].
func SliceAt(typ Type, p unsafe.Pointer, n int) Value {
	unsafeslice(typ.common(), p, n)
	s := unsafeheader.Slice{Data: p, Len: n, Cap: n}
	return Value{SliceOf(typ).common(), unsafe.Pointer(&s), flagIndir | flag(Slice)}
}