unexpected warnings on `std.native` function calls

## Versions

- VS Code Jsonnet Language Server Extension v0.3.3
- jsonnet-language-server v0.11.0

## Example Code

```jsonnet
local nextID = std.native('nextID');

{
id: nextID(),
}
```

## Error Message

```
RUNTIME ERROR: Unexpected type null, expected function
/tmp/test.jsonnet:4:7-15 object
Field "id"
During manifestation
jsonnet evaluation
```

Reproduce the example with VS Code Jsonnet Language Server Extension v0.3.3 and jsonnet-language-server v0.11.0, then trace how std.native calls are handled. Done means the shown Jsonnet code no longer produces the unexpected type null error during evaluation.

Written by the indexing model from the issue text.