aws-cdk-lib: exporting a class that implements IVpc but only looks up a vpc by Id

### Describe the feature

Having a class that is able to lookup a Vpc by it's Id and implementing `IVpc` so it can be extended with own methods and properties.

### Use Case

Doing `class MyVpc extends Vpc` will try to deploy a new Vpc to aws and that is not intended. I want to be able to extend a class that looks up Vpc by it's id in something like:

```typescript
class MyVpc extends VpcLookup {
constructor(scope: Construct, id: string, props?: VpcLookupOptions) {
super(scope, id, props);
}

get someSubnetGroup() {
this.selectSubnets({
...
})
}
}
```

### Proposed Solution

Maybe it's possible to move `Vpc.fromLookup` code/logic to inside of a seperated class constructor?

### Other Information

Alternative solution would be export [LookedUpVpc](https://github.com/aws/aws-cdk/blob/1f7075f8bd6bd3c1d760cb9e899a7cba52e2993a/packages/aws-cdk-lib/aws-ec2/lib/vpc.ts#L2218)?

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

2

### Environment details (OS name and version, etc.)

linux

Start in packages/aws-cdk-lib/aws-ec2/lib/vpc.ts, especially Vpc.fromLookup and the LookedUpVpc implementation linked in the issue. Trace how the lookup result implements IVpc and review related tests before deciding whether exporting that class or introducing a separate extensible class fits the API. Done means consumers can extend a lookup-backed VPC without synthesizing a new VPC.

Written by the indexing model from the issue text.