(cli): `cdk diff` does not detail service catalog changes

### Describe the bug

`cdk diff` only reports a url change when diffing service catalog product stacks like this:
```
[~] AWS::ServiceCatalog::CloudFormationProduct TestProduct TestProductABC
└─ [~] ProvisioningArtifactParameters
└─ @@ -3,7 +3,7 @@
[ ] "DisableTemplateValidation": false,
[ ] "Info": {
[ ] "LoadTemplateFromURL": {
[-] "Fn::Sub": "https://s3.eu-central-1.${AWS::URLSuffix}/(redacted-bucket)/(redacted-key).json"
[+] "Fn::Sub": "https://s3.eu-central-1.${AWS::URLSuffix}/(redacted-bucket)/(redacted-key).json"
[ ] }
[ ] },
```

### Expected Behavior

I would expect a full diff of the `CloudFormationProduct`

### Current Behavior

as seen above

### Reproduction Steps

Create a CloudFormationProduct, deploy it, change something, run `cdk diff`

### Possible Solution

Download the previous version of the `CloudFormationProduct` template from the S3 Bucket and diff to the current output.

### Additional Information/Context

_No response_

### CDK CLI Version

2.26.0 (build a409d63)

### Framework Version

_No response_

### Node.js Version

v16.13.0

### OS

WSL2 (Ubuntu) on Windows 11

### Language

Typescript

### Language Version

_No response_

### Other information

_No response_

Start by reproducing the reported case with a deployed CloudFormationProduct, then change it and run the cdk diff command. Trace how the CLI compares the previous and current product templates; done means cdk diff reports the actual service catalog changes rather than only a URL change.

Written by the indexing model from the issue text.