Shelley: export {to,from}AlonzoLanguage (Plutus script language conversions)

[smelc]

Changelog

- description: |
    Shelley: export {to,from}AlonzoLanguage (Plutus script language conversions)
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
  # - breaking       # the API has changed in a breaking way
  - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - refactoring    # QoL changes
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

Required to adapt cardano-node to #729

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• Self-reviewed the diff

[carbolymer]

I think we should replace those two function with Inject instances.

[smelc]

@carbolymer> I disagree, I think we should keep Inject for conversions between eons; otherwise upon seeing a call to inject in the code we won't easily know what it's about.

[carbolymer]

That's not what is Inject for in general. It's used widely in ledger codebase for conversion between isomorphic types.

[smelc]

@carbolymer> is the ledger a model codebase in terms of ease-of-understanding 😉?

[carbolymer]

LGTM