SCP-2771: Plutus V2 interface

[michaelpj]

This is a first attempt at a V2 ledger interface.

• It re-exports almost everything from V1.
• It has new definitions of TxInfo and ScriptContext (which depends on TxInfo), as well as the functions that operate on TxInfo, and the envelope type.
• Changes to TxInfo:
  • Use Map for the maps
  • Add redeemer map

I have not changed anything to use it: in the future we'll want to do that, but probably the plutus-ledger stuff should happen after we split the repo.

Pre-submit checklist:

• Branch
  • Tests are provided (if possible)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
  • Relevant tickets are mentioned in commit messages
  • Formatting, materialized Nix files, PNG optimization, etc. are updated
• PR
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested

[JaredCorduan]

This is great, thanks!

[michaelpj]

Okay, in it goes.