ABCI 2.0: Spec work

[sergio-mena]

Tasks:

• Finish RFC-017: add section on vote extension upgrade path #8484
• Turn RFC017 into part of the spec
• Uncomment all parts related to vote extensions, and FinalizeBlock from the spec.
• Re-merge the spec as of v0.36.x into feature/abci++vef and go through the conflicts (goal: make sure we didn't forget anything)
• Follow Restore Commit to the ABCI++ spec, and other late modifications #8796 and make sure the changes are present in the spec
  • Restore data field in Commit
  • Rename Misbehaviour to ByzantineValidators (done already?)
• Final read of spec for overall coherence
  • Compare it with the version living in v0.36.x

DoD:

• Out of all solutions proposed in RFC017, the one implemented (sub-optimal storage) is now part of the spec
• Spec is updated to ABCI 2.0 (very similar to the one in v0.36.x
• Spec is complete and proof-read
• Spec methods and data structures match the corresponding protobufs