Feature Request: Support for multi-file xml schemas

I have an XSD where the file serves as the top-level file and contains the root-element definition, but it includes directly and inderictly many other XSD files.

For example I have
```

```

No files or tests are named. Start by locating the entry point that loads the top-level XSD and trace how schema includes are resolved. Done means direct and indirect included XSD files are handled when generating forms; add or update coverage for the shown include case if a relevant test area exists.

Written by the indexing model from the issue text.