Add Ior#mergeWith and Align#alignMergeWith

[nigredo-tori]

These are versions of Ior#merge and Align#alignCombine that use explicit functions rather than Semigroup instances.

Motivation: alignMergeWith is useful in cases where the logic in case of a "conflict" doesn't match the default Semigroup instance. It is also useful in places where relying on a specific Semigroup makes the code brittle. For example, when combining nested Maps and NonEmptyMaps, changing NonEmptyMap to Map might introduce subtle errors due to different Semigroup semantics - see #3377.