Pull all 'show' routines into `X.Show`

[JacquesCarette]

There are a number of places where Data.String (and friends) are used merely for show. This introduces spurious dependencies. I think all of these should be moved to sub-modules.

[Taneb]

Isn't this already the case? There's already-deprecated shows in Data.Rational and Data.Integer but I can't see any others outside of X.Show modules

[JacquesCarette]

See PR #2016 for a number of examples.