This adds test cases for N(data length) in {1, 2, 4, 32}.
This tests real and complex input cases. It also tests polar and
non-polar output case. The reference(expected) numbers were obtained
using fft() of Matlab R2018b. Finally the inverse transform is
compared is compared with original inputs for correctness.

No tests are there for non powers of 2 data length cases yet as
the implementation is going to change for such cases to behave
exactly like Matlab/Octave.

Change-Id: I580e70c0e30a8bc4a5d388aaa522e4583283be67
Reviewed-on: https://gerrit.libreoffice.org/68285
Tested-by: Jenkins
Reviewed-by: Dennis Francis <dennis.francis@collabora.com>