Introduce LF 2.x

[paulbrauner-da]

Introduce a new major version of LF that is backwards incompatible with LF 1.x.

• [x] Introduce a new major version in the proto, compiler and engine. Keep it backwards compatible for now. #17348
• [x] Stop assuming backwards compatibility of the 2.x versions (remove total ordering over version), update code accordingly.
  • [x] In compiler
  • [x] In engine
• [x] Make deprecated features incompatible with 2.x, make new features (like right-to-left evaluation) 2.x-only
• [x] Split parts of the engine and the compiler between 1.x and 2.x where that makes sense (e.g. speedy, decoders, encoders)
• [ ] Clean up the 2.x proto, introduce breaking changes if necessary
• [ ] After Daml 3:
  • [x] modify canton 3.x to default to LF 2
  • [x] create a main-2.x git branch
  • [x] delete everything 1.x related in the main branch. Tracked in https://github.com/digital-asset/daml/issues/18240.

See this incomplete design doc for a description of the current state. See these slides for a friendlier version of the checklist above.