Implement ValidationContext::host_consensus_state() for IbcExecutionContext

[plafer]

Before we can implement this, @preston-evans98 needs to define the protobuf definition of a SovereignConsensusState that represents sovereign SDK chains.

Once that's done, we can implement the method by

1. querying the relevant parts of our state
2. construct a SovereignConsensusState and return it

[preston-evans98]

Thanks for the heads up @plafer. Can you link any docs to help me understand exactly what guarantees ConsensusState needs to provide?

[plafer]

Sure!

• Our ConsensusState trait that all consensus states implement
  • To be clear, our "domain type" (which is derived from the "raw" generated protobuf type) is what implements this trait
  • In the Sovereign's case, root() would return the rollup's root. I guess we'd never need access to the DA's root (other than when we're updating the client, which isn't done using this interface).
• The protobuf definition of the Tendermint ConsensusState
  • Probably useful as an example
• Official docs on ConsensusState
  • This is just extra; the IBC standard isn't always up to date nor very clear

Let me know if you need anything else

[preston-evans98]

This is perfect, thanks a ton!