`aws_stepfunctions`: Programmatic IO

### Describe the feature

One of the most frustrating areas when defining step functions is defining how values are passed between states (e.g. [`JsonPath`](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_stepfunctions.JsonPath.html)).

This could be greatly improved if states had properties to get their input and outputs.

### Use Case

```
const myPass = new sfn.Pass(this, 'MyPassState', {
parameters: {
'someValue.$': '$$.Execution.Input'
},
});
const mySfn = new sfn.StateMachine(this, 'MyStepFunction', {
definition: myPass,
timeout: cdk.Duration.hours(24)
});
```

### Proposed Solution

```
const mySfn = new sfn.StateMachine(this, 'MyStepFunction', {
timeout: cdk.Duration.hours(24)
});
const myPass = new sfn.Pass(this, 'MyPassState', {
parameters: {
'myValue': mySfn.input,
},
});
mySfn.definition = myPass;
```

### Other Information

Fixing this might be difficult, I just want to highlight this problem and see if others also experience it. Any programmatic solution would be a great improvement over using `JsonPath`s directly.

### Acknowledgements

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

### CDK version used

2.132.1

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

Linux 6.5.0-21-generic #21~22.04.1-Ubuntu x86_64 GNU/Linux

Start with the aws_stepfunctions Pass and StateMachine entry points and the JsonPath API referenced in the issue. Clarify the intended input and output semantics and the breaking-change boundaries before implementation. Done should let the shown use case express state data programmatically instead of embedding JsonPath strings.

Written by the indexing model from the issue text.