Using itk::VectorImage instead of itk::Image<Vector<...

Using itk::VectorImage instead of itk::Image (and the corresponding itk::Dream3DImage) with vector components would allow to not hardcode the number of dimension for vectors, and therefore not limit the user to a small number of vector images that can be processed (currently only vectors of dimension 2 and 3 are accepted).

Start by locating the uses of itk::Image and itk::Dream3DImage that restrict vector components to dimensions 2 and 3. Trace the related image-processing entry points and tests, then define the scope and validation needed for itk::VectorImage to support arbitrary vector dimensions.

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