Including original Numpy Sort methods

[gpolov-personal]

Description

Include in the mxnet.numpy interface functions from the numpy package

• numpy.sort(a, axis =1, kind=None , order=None ): This is a package function

• numpy.ndarray.sort(axis=-1, kind=None , order=None): This is an instance method

• numpy.argsort(a, axis=-1 , kind=None, order=None): This is a package function

The idea is to use them within a autograd.record() context and being able to compute the gradient of functions that use them.

References

• numpy.argsort: https://docs.scipy.org/doc/numpy/reference/generated/numpy.argsort.html#numpy.argsort
• numpy.sort:
  https://docs.scipy.org/doc/numpy/reference/generated/numpy.sort.html#numpy.sort
• numpy.ndarray.sort: https://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.sort.html#numpy.ndarray.sort

Thank you very much

[sxjscience]

I think there is an open PR that tries to add sort: #16750

[haojin2]

PR for np.argsort: #16949

[eric-haibin-lin]

looks like the feature is added already