Add constructor functions for use by cw-sdk

[larry0x]

As pointed out by #1552, two query response types (bank::SupplyResponse and wasm::ContractInfoResponse) are marked as #[non_exhaustive] and thus cannot be constructed directly.

This is not a problem for wasmd, as they are created by deserialization. However for cw-sdk I do need to construct these responses in Rust code.

Simply adding a new function is not a satisfactory solution, as @webmaster128 pointed out, we would not be able to add new fields to the response type without changing the function signature.

The solution I'm going with here is to add an option cw_sdk feature, and the constructor functions only exist if cw_sdk feature is enabled.

[webmaster128]

I think this is a better solution to the problem as it is more universal and does not make too many assumptions about the runtime that is trying to construct the query responses.

[larry0x]

Closing this as #1560 is the preferred solution.