Add support for wrapping types in deserialization

[quinchs]

Summary

This PR adds another step in the deserialization pipeline which support wrapping types, ex: Nullable<T>, Option<T>, etc. It also fixes a bug with value type deserialization due to expression initialization by adding an explicit box operation.

[scotttrinh]

Code makes sense to me! Is there any easy test case we can add at least for Nullable<T> to exercise this behavior?

[quinchs]

Added!