Expose EraTxWits, TxDats, and functions for converting datums and scripts to JSON

[palas]

Changelog

- description: |
    Exposed `Language`, `Plutus`, `Script`, `getNativeScript`, `languageToText`, `plutusBinary`, `plutusScriptLanguage`, `serializeAsHexText`, `showTimelock` in `Cardano.Api.Ledger`, and `AlonzoEraOnwardsConstraints` in `Cardano.Api`
  type:
  - feature

Context

friendlyTxBodyImpl wasn't exposing information about datums nor redeemers. In order to address that, it is necessary to expose types through the cardano-api to be used by cardano-cli.

How to trust this PR

I would look at the structure of the JSON that is generated mainly, and check whether the functions and types are exported in the right places. Also probably good to look at this PR in conjunction with IntersectMBO/cardano-cli#977

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff