V2 parser

[kubukoz]

• Scanner: V2 Parser: Add scanner #340
• Parser
  • ???
  • Conversion to v1 format
  • Parity tests with v1
    • include v2 parser test in all generative tests
    • positive cases should match to the same result (modulo comments)
    • same as above, but comments should be fixed
  • Identify initial usecase for migration
    • Diagnostics? Seems like a way to get immediate feedback about how good this is, but could produce a lot of noise
  • Treat unclosed string literals as broken (scanner reports these as normal string literal tokens)