Vector4i doesn't implement "into Variant"

Vector4i objects don't have means to convert to Variant.

Here is an example of what I'd expect to work:
```
let vec4i = Vector4i::new(0, 0, 0, 0);
let variant = Variant::from(vec4i);
```

But doing so produces the following error:
```
the trait bound `godot::prelude::Vector4i: EngineEnum` is not satisfied
```

