Allow DynamicArray to map over const range

[skgbanga]

Hello,

I have a use case in which I iterative over a const range, do some transformation on it and store it another range. The original range is const float.

I modelled this as:

  using FloatArray = enoki::Array<float, 8, true, enoki::RoundingMode::Default>;

  enoki::DynamicArray<const FloatArray> input;
  enoki::DynamicArray<FloatArray> destination;

and I do DynamicArray::map over my float ranges like this:

void foo(const float* input, size_t s) {
  input = enoki::DynamicArray<const FloatArray>(input, s);
}

However, map signature is:

static Derived map(void *ptr, size_t size) {

and I get a compiler error that I am casting away my constness.

If I change this to:

    template <typename T>
    static Derived map(T *ptr, size_t size) {

everything works out since now template type T has constness in it.

Would you be open to accept this change as a PR?