Specialize sconcat for the Semigroup instance of First

The default sconcat implementation is overly strict in the spine in the specific case of Data.Semigroup.First

>>> sconcat $ First () :| undefined
First {getFirst = *** Exception: Prelude.undefined
...

A very simple, lazier, implementation of sconcat as sconcat (x :| _) = x would get rid of this problem. This can also have performance benefits when the spine takes a long time to compute.

>>> sconcat $ First () :| undefined
First {getFirst = ()}