Panic when processing type aliases to owned resource handles

### Summary

wit-bindgen panics when processing WIT files that contain type aliases to resource handles (e.g., `type my-handle = own`).

### Environment

- **wit-bindgen version**: 0.47.0
- **Affected component:** wit-bindgen-core
- **OS**: Ubuntu 22.04, x86-64

### Steps to Reproduce

1. Create a minimal WIT file

Save the following as `test.wit`:

```wit
package poc:demo;

interface db {
resource database {
constructor();
query: func(sql: string) -> string;
}

// Type alias to owned resource handle
type db-handle = own;

connect: func() -> db-handle;
}

world test-world {
export db;
}
```

2. Run wit-bindgen

```bash
wit-bindgen rust --out-dir /tmp/test test.wit
```

3. Observe the panic

```
thread 'main' panicked at /home/runner/work/wit-bindgen/wit-bindgen/crates/core/src/lib.rs:183:39:
handle types do not require definition
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```