>>> x = 1j * torch.arange(8).view(2, 2, 2)
>>> torch.flip(x, [0, 1])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: "flip_cpu" not implemented for 'ComplexFloat'

This task would most likely just involve extending the dispatch to complex numbers.

Once torch.flip is added for complex, torch.rot90 would also start working for complex. so, please add test for rot90 as well.

cc @ezyang @anjali411 @dylanbespalko