Bug in element coordinate replacement if cubes loop pattern is chosen

The function _compute_micro_element_coordinates computes the element coordinates from the loop counters. To enable vectorization, the replacement is currently done in a custom code node.

The issue arises during loop cutting for the cubes loop, since loops with end - start are automatically replaced with their loop bodies by pystencils. However, the custom code node requires the presence of the loop counter, which has been removed through the loop cutting.

A possible solution would be to not remove these short loops during cutting.