Implementation of histogram with sycl kernel

[AlexanderKalistratov]

Implemention of histogram with sycl_kernel.
This PR adds generic histogram kernel which can be used in the future to implement other versions of histogram such as bincount, histogram2d and histogramdd or specialize kernel for special cases like uniform bins.

sycl kernel covers only specific datatype and usm memory types. Unsupported cases are covered by additional copy.

[oleksandr-pavlyk]

Because a may be usm_ndarray (according to docstring), it is not safe to use a.astype, since usm_ndarray does not implement such a method. Instead dpctl.tensor.astype should be used, or support for such input types should not be advertised.

[AlexanderKalistratov]

Done, replaced with dpnp.astype(a, ...)

[oleksandr-pavlyk]

Quick validation via independent implementation:

def histogram1d_impl_tensor(data : dpt.usm_ndarray, bins : dpt.usm_ndarray) -> dpt.usm_ndarray:
    assert data.ndim == 1 
    assert bins.ndim == 1
    assert bins.shape[0] > 1
    bin_idx = dpt.searchsorted(bins, data)
    _, c = dpt.unique_counts(dpt.sort(bin_idx))
    return c

In [22]: x = dpnp.random.randn(10**7).get_array()

In [23]: bins = dpnp.asarray([-10, -4, -3, -2, -1, -0.5, -0.25, 0, 0.25, 0.5, 1, 2, 3, 4, 6], dtype=x.dtype).get_array()

In [24]: %time c, _ = dpnp.histogram(dpnp.asarray(x), bins=dpnp.asarray(bins)); print(c)
[    284   13222  214243 1359725 1497540  927356  987069  987352  927886
 1498601 1358597  214704   13114     307]
CPU times: user 10.6 ms, sys: 10.4 ms, total: 21 ms
Wall time: 15.2 ms

In [25]: %time c = histogram1d_impl_tensor(x, bins=bins); print(c)
[    284   13222  214243 1359725 1497540  927356  987069  987352  927886
 1498601 1358597  214704   13114     307]
CPU times: user 711 ms, sys: 581 ms, total: 1.29 s
Wall time: 396 ms

[oleksandr-pavlyk]

Suggested change

	#include "utils/type_dispatch.hpp"
	#include "dpctl4pybind11.hpp"
	#include "utils/type_dispatch.hpp"

[AlexanderKalistratov]

Done