Add contract sanity checking during build / release

[maurolacy]

Let's add sanity checking (check exports, imports, deterministic middleware, ...) to wasm-compiled (.wasm) smart contracts.

An easy way to do this would be to add a simple / dummy integration test for the contract. Given that compiling and running integration tests is expensive, we could run these tests in the CI only during the contract building / release step.

An alternative or complement to this would be to use a small utility to just compile the contract. Something similar to module_size. Perhaps with some additional checks / validations.

Let's do this for cosmwasm-plus contracts, and also cosmwasm and cosmwasm-examples contracts.