(ec2-alpha): Expose `VpcPeeringRole` role name

### Describe the feature

`createAcceptorVpcRole` is a method that creates the role, but then the requester needs the same role to be specified via `peerRoleArn`.

This then introduces a "magic string" anti-pattern.

### Use Case

To avoid magic strings.

### Proposed Solution

Would be great to either have the role name available via some const, or even better have another method:

```
createRequestorPeerRole: IRole
```

And then `createPeeringConnection` would accept `peerRole`, instead of `peerRoleArn`.

Example:

```TypeScript
requestorVpc.createPeeringConnection("Peering", {
acceptorVpc,
peerRole: requestorVpc.createRequestorPeerRole(awsAccount: string)
});
```

### Other Information

https://github.com/aws/aws-cdk/blob/31bf1bfb70adba820281407c11400ed6f744dead/packages/%40aws-cdk/aws-ec2-alpha/lib/vpc-v2-base.ts#L624-L628

### Acknowledgements

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

### AWS CDK Library version (aws-cdk-lib)

N/A

### AWS CDK CLI version

N/A

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

N/A

Start in packages/@aws-cdk/aws-ec2-alpha/lib/vpc-v2-base.ts at the referenced lines, then trace createAcceptorVpcRole and createPeeringConnection. Compare the proposed role-name constant and peer-role API options, and define completion as allowing the requester to reuse the created role without a magic string while accounting for the possible breaking change.

Written by the indexing model from the issue text.