[#159] Make it possible to define a type with FA2 annotations

Description

Problem: See FA2. One day we will inevitably have to implement a contract conforming to it in Lorentz or Indigo. Look at the total_supply type:

(pair %total_supply
  (list %token_ids nat)
  (contract %callback
    (list
      (pair
        (nat %token_id)
        (nat %total_supply)
      )
    )
  )
)

There are two problems:

1. snake_case annotations.
2. Field annotations for things that are not entrypoints.

Currently we can't generate such things.

Solution: Add ability to generate field annotation for record type in entrypoint sum types.

Related issue(s)

Resolves #159 (closed)

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