ENH: Add initial annotations to np.core.multiarray

[BvB93]

This PR adds initial annotations to np.core.multiarray.

DType-support is still far from comprehensive, but at the very least all types that can be parametrized w.r.t. np.generic are now automatically recognized.

Examples

from typing import TYPE_CHECKING
import numpy as np

AR_f8 = np.array([1], dtype=np.float64)
AR_f8_copy = np.array(AR_f8)
AR_f8_0d = np.array(np.float64())

if TYPE_CHECKING:
    # Revealed local types are:
    #     AR_f8: numpy.ndarray[Any, numpy.dtype[numpy.floating*[numpy.typing._64Bit*]]]
    #     AR_f8_0d: numpy.ndarray[Any, numpy.dtype[numpy.floating*[numpy.typing._64Bit*]]]
    #     AR_f8_copy: numpy.ndarray[Any, numpy.dtype[numpy.floating*[numpy.typing._64Bit*]]]
    reveal_locals()

[BvB93]

This is a common overload pattern:

1. Array-likes that can be parametrized w.r.t. generic
2. All other array-likes
3. DType-likes that can be parametrized w.r.t. generic
4. All other DType-likes

[BvB93]

Any comments on this PR?

[charris]

Thanks Bas.