(ec2): Support regional NAT gateways in Vpc construct

### Describe the feature

Add support for regional NAT gateways to the VPC construct

https://aws.amazon.com/blogs/networking-and-content-delivery/introducing-amazon-vpc-regional-nat-gateway/
https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-resource-ec2-natgateway.html

### Use Case

Simpler setup than zonal gateways

### Proposed Solution

maybe simple a `natGatewayType` property for the VPC construct?

### Other Information

You can workaround it for now by doing this

```typescript
const vpc = new ec2.Vpc(this, 'Vpc', {
vpcName: 'foobar',
maxAzs: 3,
natGateways: 1, // Using regional so we only need one
],
});
this.vpc = vpc;

// FIXME: undo this once it is supported by CDK
vpc.node.findAll().forEach((child) => {
if (child instanceof ec2.CfnNatGateway) {
child.addPropertyOverride('AvailabilityMode', 'regional');
child.addPropertyOverride('VpcId', vpc.vpcId);
child.addPropertyDeletionOverride('SubnetId');
}
});
```

### Acknowledgements

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

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

aws-cdk-lib@2.227.0

### AWS CDK CLI version

2.1033.0 (build 1ec3310)

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

Ubuntu 25.04

Start at the TypeScript ec2.Vpc construct and its NAT gateway handling. Read the linked regional NAT gateway and CloudFormation NATGateway documentation, then compare the existing workaround with the construct's synthesized resource. Done means a VPC can request regional NAT gateways through the proposed configuration and synthesis produces the corresponding regional resource without the workaround.

Written by the indexing model from the issue text.