[#330] add wrap and unwrap expressions for sum types constructors

Description

Adds expression to Indigo to perform wrapping and unwrapping of values to/from single-field constructors of sum types.

For example:

data T = A Bool | B Natural
  deriving stock Generic
  deriving anyclass (IsoValue, HasAnnotation)

exampleContract :: IndigoContract Bool T
exampleContract param = defContract do
  storageVar @T =: wrap #cA param
  _boolean <- new$ unwrap #cA (storageVar @T)
  return ()

Related issue(s)

Resolves #330 (closed)

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