UniqueDFM: alter should preserve insertion order

Zubinrequested to merge
wip/27532 into master

UniqueDFM: alter should preserve insertion order

Before it always inserting new elements at the end. This is problematic because instances get inserted into the map with alterF, which can change ordering of how instances are printed with :info depending on the order in which we consult interfaces

I expect alter id k = id and alter (fmap f) k = adjust f k. Moving keys to the end breaks that (adjust already preserves position).

Fixes #27532 (closed)

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