Typecheck corebindings lazily during bytecode generation

This delays typechecking the corebindings until the bytecode generation
happens.

We also avoid allocating a thunk that is retained by `unsafeInterleaveIO`.
In general, we shouldn't retain values of the hydrated `Type`, as not evaluating
the bytecode object keeps it alive.

It is better if we retain the unhydrated `IfaceType`.

See Note [Hydrating Modules]