fix flaky test: boolean index and fix bugs

[Alicia1529]

1. fix the problem in issue Flaky test: test_numpy_op.test_npi_boolean_assign #17219:
   As the variable val is a mxnet.numpy.array, the operation np_data[np_mask] = val actually fall back to mxnet operation
2. handle boolean indexing on 0-d array and index as primitive boolean type. For example:

>>> from mxnet import np, npx
>>> npx.set_np()
>>> import numpy as _np
>>> mx_a = np.array(1)
>>> np_a = _np.array(1)
>>> mx_a[True]
array([1.])
>>> mx_a[False]
array([])
>>> np_a[True]
array([1])
>>> np_a[False]
array([], dtype=int64)