Fix#12355.
In the issue, it was reported that the `reorder_items` has quadratic (or
worse...) behavior with certain simple parametrizations. After some
debugging I found that the problem happens because the "Fix
items_by_argkey order" loop keeps adding the same item to the deque,
and it reaches epic sizes which causes the slowdown.
I don't claim to understand how the `reorder_items` algorithm works, but
if as far as I understand, if an item already exists in the deque, the
correct thing to do is to move it to the front. Since a deque doesn't
have such an (efficient) operation, this switches to `OrderedDict` which
can efficiently append from both sides, deduplicate and move to front.
e89d23b247