We currently allow two different import styles for our monopackage:

```ts
import { aws_ec2 } from 'aws-cdk-lib';
import * as aws_ec2 from 'aws-cdk-lib/aws-ec2';
```

However, the way this is currently implemented breaks the source
analysis performed by Rosetta on examples. Rosetta will only be
able to trace the first of these to the submodule that is being
imported. The second style actually is a completely different JavaScript
file that "represents" the export, and the tracing will break.

Today these resolve to:

```
import { aws_ec2 } from "aws-cdk-lib";

------> aws-cdk-lib/lib/aws-ec2/index.ts

import * as aws_ec2 from "aws-cdk-lib/aws-ec2";

------> aws-cdk-lib/aws-ec2.ts
```

This PR changes the layout of the package generated by `ubergen` to have
the submodule directories at the root, so that the imports resolve the
same:

```ts
// aws-cdk-lib/index.ts
export * as aws_ec2 from './aws-ec2';

// aws-cdk-lib/aws-ec2/index.ts
module_contents_here();
```

This means we now collect all submodules into the *root* of `aws-cdk-lib` and `monocdk`, instead of into
the `lib` subdirectory. It makes the gitignore config slightly different from the ones we usually have (but arguably better).

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*