Add Any message with blanket implementation

[webmaster128]

Closes #1924

[chipshort]

I removed the Stargate variant here, since Any will take over that role and 2.0 is our chance to do these kinds of breaking changes. I also added a changelog and migrating entry.
One thing I am wondering about atm: We could add a #[serde(rename = "stargate")] here. That way the json representation will become the same as the previous Stargate message and no changes to wasmd would be needed (otherwise wasmd would have to support both anyways for backwards compatibility).

[webmaster128]

One thing I am wondering about atm: We could add a #[serde(rename = "stargate")] here. That way the json representation will become the same as the previous Stargate message and no changes to wasmd would be needed (otherwise wasmd would have to support both anyways for backwards compatibility).

I tend to agree. But can we move this consolidation to the wasmvm codebase somehow? I.e. deserialize "any" and "stargate" into a single field in the struct? This would create a cleaner JSON interface for a future where we have different host environments.

[chipshort]

I agree, that would be even better. It can be done, but I think only with a custom unmarshalling function in wasmvm (or by having both fields, but that seems a bit ugly). I'll prepare a PR

[webmaster128]

I think this is ready assuming we solve the "stargate"/"any" cases ion the Go side

[chipshort]

Yes, this is ready. "stargate" / "any" handling is also ready in CosmWasm/wasmvm#468