Filepath and module path can differ

The file path (eg. `/my/inlude/path/to/file.effekt`) and the module path (e.g. `module path/file`) can differ.

Now assume we include an import statement in another file:

```
import path/to/file
```

Typechecking and compilation might succeed since the file is correctly resolved. The generated JavaScript file however uses the `declared` path on the module, not the actual path. That is, it generates a file `path_file.js`. The import will look for `path_to_file.js`, which it cannot find.

We either should error / warn if there is this mismatch or exclude paths in module declarations altogether.