Accessing Instance.Context reports missing DLL entry point.

Calling `Context` on an instance of `Instance`

i.e.

```.cs
    //...
    var instance = new Instance(wasm, printFn, memoryImport);
    InstanceContext context = instance.Context;
```

**gives the error:**

```
`Unable to find an entry point named 'wasmer_instance_context_get' in DLL 'wasmer_runtime_c_api'.
```