rebuild! if we migrate from another gem to closure_tree might ignore ordering

[krtschmr]

coming from awesome_nested_set we use lft for ordering.
i checked the rebuild! method and it looks like it's calling children which then might be rendered randomly by our DB.
we then recreate the tree for each children, but this means that the position might change.

children.find_each { |c| c.rebuild!(true) }

https://github.com/ClosureTree/closure_tree/blob/07f4dfdac48765a60a786a5dfedaffb1d1e242be/lib/closure_tree/hierarchy_maintenance.rb#L65:L89

example

before:

1, lft: 1, position: nil
2, lft: 5, position: nil
3, lft: 4, position: nil
4, lft: 3, position: nil
5, lft: 2, position: nil

If we call .children we might get in return 1,2,3,4,5 but we actually want to get 1,5,4,3,2.

the tree then could be created like

1, lft: 1, position: 1
2, lft: 5, position: 2
3, lft: 4, position: 3
4, lft: 3, position: 4
5, lft: 2, position: 5