Add support for fftshift function from NumPy

[belyan]

I need this function in my project, but it is missed in math,js now, so I forced to import fftshift library to use it.

Here is documentation of this function from NumPy site:
https://numpy.org/doc/stable/reference/generated/numpy.fft.fftshift.html

Here is source code on Python:
https://github.com/numpy/numpy/blob/v1.26.0/numpy/fft/helper.py#L19-L73

Here is an example of implementation on JavaScript:
https://unpkg.com/browse/fftshift@1.0.1/build/index.js

[josdejong]

Thaks for your suggestion Yuri!

Anyone interested in implementing a function fftshift? Help would be welcome.