CreateOutputFFTMethods requires a image creator that can take an ImgFactory #650
Description
As described in this forum post, CreateOutputFFTMethods will fail when it is asked to create a large image, as it always assumes that the image can be an ArrayImg.
We need an Op that can take an ImgFactory as a parameter, so that CreateOutputFFTMethods can decide whether to make a CellImg or an ArrayImg. Or, at least, we can delegate the ImgFactory choice to Util.getSuitableImgFactory. And then CreateOutputFFTMethods needs to call it.
(And we should also make this change in ImageJ-Ops2 😁)