CDK:Alarm constructor statistic prop doesn't use Cfn extendedStatistic for IQM

### Describe the bug

When creating an alarm with IQM, eg
```
new Alarm(..., {
...,
metric: new Metric({
...,
statistic: Stats.IQM,
}),
})
```

### Expected Behavior

```
"ExtendedStatistic": "IQM",
```

### Current Behavior

```
"Statistic": "IQM",
```
which is not valid

### Reproduction Steps

```
import { Stack, type StackProps } from "aws-cdk-lib";
import { Alarm, ComparisonOperator, Metric, Stats } from "aws-cdk-lib/aws-cloudwatch";
import { Construct } from "constructs";

export class TestStack extends Stack {
constructor(scope: Construct, props?: StackProps) {
super(scope, "test-stack", props);

new Alarm(this, "MockAlarm", {
evaluationPeriods: 1,
threshold: 0,
comparisonOperator: ComparisonOperator.GREATER_THAN_THRESHOLD,
metric: new Metric({
namespace: "MOCK",
metricName: "TEST",
statistic: Stats.IQM,
}),
});
}
}

```

### Possible Solution

_No response_

### Additional Information/Context

This used to work on cdk 2.45.0

### CDK CLI Version

2.122.0 (build 7e77e02)

### Framework Version

_No response_

### Node.js Version

v20.9.0

### OS

Ubuntu 23.10

### Language

TypeScript

### Language Version

5.3.3

### Other information

_No response_

Start with the provided TypeScript reproduction and inspect the synthesized CloudFormation for MockAlarm. Trace how Metric statistic is mapped into the alarm properties, then verify that Stats.IQM produces ExtendedStatistic rather than Statistic. Done means the reproduction synthesizes valid output with "ExtendedStatistic": "IQM" and includes regression coverage if the relevant test location is identified.

Written by the indexing model from the issue text.