1. Removed unused usm_ndarray._clone static C-only method
2. Removed _dispatch* utilities
3. Used direct calls to unary/binary operators in implementation
   of special methods

Provide cabs private method implementating abs for complex types, paying
attention to array-API mandated special values.

To work-around gh-1279, use std::hypot to compute value for finite inputs.
Compile with -DUSE_STD_ABS_FOR_COMPLEX_TYPES to use std::abs(z) instead of
std::hypot(std::real(z), std::imag(z)).

This change provides private method csqrt to evaluate square-root
for complex types. It handles special values as mandated by array API.

The finite input, it provides its own implementation based on std::hypot
and std::sqrt for real types instead of calling std::sqrt on finite
input of complex type.

Compile with -DUSE_STD_SQRT_FOR_COMPLEX_TYPES to use std::sqrt instead
of custom implementation.

Cursory performance study suggests that custom implementation is at least
not worse than std::sqrt one.

This utility function is based on symmetric check, unlike numpy.allclose,
and verifies that abs(x1-x2) < atol + rtol * max(abs(x1), abs(x2))

This way allclose(x1, x2) is symmetric, and allclose(x1,x2) implies
allclose(x2, x1).

1. Aligned default values with those of np.allclose
2. Replaced less test with less_equal to align with NumPy.

Also added tests for early exits to improve coverage.

This changes builds up on gh-1265 and takes into account queue
from the pre-allocated buffer, if provided.

This improves accuracy at extremes of supported range.

Use sycl:: namespace ldexp and ilogb to prevent problem
with VS 2017 headers.

ilogb would have to pay attention to correctly computing
scale of denormal floats, while simpler code suffices.

Also use unscaled version in most cases, and scaled version
only for very large inputs.

We work around issues with these functions when their implementation
is taken from VS 2017 headers on Windows though.