Remove unused operator import
Factor out Injectable from Prismable

I realized that I don’t know how to `pcoerce` the type `[a]` from an AValue, but
there's a pretty natural injection. Well, it's not really an injective because
Objects could also get in there. Not sure what to call this. `Representable`?

Anyway, it also lets me define `Injectable (Set AValue) a` which just creates a
singleton object.
Avoid shadowing by using `op` instead of `o`
Precedence fix for `(.:)` precedence change
Make liberal use of pinject for `(Set AValue)`
Teach Delta to `OStrContain`, `OStrSplitRegExp`, and `OStrSplitStrExp`

This involved refactoring the `liftBinaryOpBot` to depend on one which allows me
to explicitly set the output bottom value. Object’s have a couple different
reasonable “default” values. In this case, I needed the empty object.