dwidenoise: Variance-stabilising transform

[Lestropie]

Content to list publicly here now as I don't think it's novel:

https://www.sciencedirect.com/science/article/pii/S1053811920303384

Where an input noise level map is provided (#2274), data imported from voxels within a patch into the Casorati matrix can be scaled by their respective estimated noise levels, such that the variance of all columns should be approximately unity. This should correct for non-stationarity of noise level within patches that cover are physically large in size.

[Lestropie]

Added in a680743 as part of #3029.

[Lestropie]

It's quite likely that this mechanism will require greater mathematical care than it has thus far been afforded; eg. https://arxiv.org/pdf/1811.02201.