Support Local Step Functions Workflow Studio Integration for CDK Users

## Current Situation
Currently, the AWS Toolkit for VS Code provides Step Functions Workflow Studio through the App Composer integration, which generates SAM-compatible state machine definitions. While this is great for SAM users, CDK users cannot directly benefit from this visual workflow editor.

## Problem
When working with Step Functions in CDK:
1. You have to write ASL JSON definitions manually or maintain them in separate files
2. There's no visual editor integration for CDK-based state machines
3. The current Workflow Studio integration only works for SAM applications, generating complete SAM applications rather than just the workflow definition

## Proposed Solution
Add support for CDK workflows in the VS Code Workflow Studio by:
1. Allowing users to edit just the workflow definition part without generating a complete SAM application
2. Providing an option to export the ASL definition in a format that can be directly used with CDK's [`StateMachine`](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_stepfunctions.StateMachine.html) construct
3. Supporting round-trip editing where CDK users can:
- Open existing ASL definitions in Workflow Studio
- Make visual changes
- Save back to their CDK project

## Additional Context
The community has recognized this need, leading to third-party solutions like [@mbonig/state-machine](https://github.com/mbonig/state-machine). However, having this capability built into the AWS Toolkit would provide a more integrated and maintainable solution.

Start by tracing the existing App Composer and SAM Workflow Studio integration in the AWS Toolkit for VS Code. Compare its generated state machine definitions with the CDK StateMachine construct and ASL definitions; done should support editing only the workflow definition, exporting it for CDK, and round-trip saves to a CDK project.

Written by the indexing model from the issue text.