These are newtype wrappers with different Monoid instances. This is for
following our more recent approach to the Monoid instances of our config
types where rather than having custom mappen methods, we derive generic
Monoid/Semigroup instances and rely on using special types like NubList
for individual fields that need different mappend behaviour.

The Map type has mappend behaviour that is not usually what we want for
our configuration types. The normal Map mappend prefers the first
argument over the second when keys overlap between the two maps. We
normally want later things to either override or to extend, like our
normal Flag (like Last) monoid or list monoid. So MapLast is a Map with
Flag/Last-like behaviour, ie flip Map.union, while MapMappend is a Map
that merges values when keys overlap, ie Map.unionWith (<>). The latter
helps when the Map values are lists or further records.