C API: creating a module should require an engine, not a store

[fitzgen]

We made changes to the Rust API so that creating a module requires an engine, not a store. However, we didn't propagate this change out to the C API (nor the python API and I assume not to the go or .NET APIs either).

We should do this. It might require using non-standard wasmtime.h functions, unless we convince upstream to make this change as well.

[yurydelendik]

We made changes to the Rust API so that creating a module requires an engine, not a store.

Yeah, the reason was HostRef. Now since it is gone we can change signature of wasmtime_module_new.