SI-7443 Use typeclass instance for {Range,NumericRange}.sum

Previously both Range and NumeriRange used formula for sum of elements
of arithmetic series and thus always assumed that provided Numeric is
regular one.
Bug is now fixed by conservatively checking if Numeric is one of
default ones and the formula still holds.
Merge pull request #3124 from DarkDimius/fix-7443

 Fix SI-7443 Range.sum ignoring Numeric argument and always assuming default 'plus' implementation