Feature Define Step Command generates async step definition methods

[clrudolphi]

🤔 What's changed?

Enhanced the Define Steps command to support generating method stubs that are async.
This honors the reqnroll.json Trace setting introduced in Reqnroll PR#876.
The DefineStep dialog box now has a check box to indicate whether to use async methods.

⚡️ What's your motivation?

Developer productivity by eliminating the need to edit the generated stubs to support async.

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

Haven't changed any documentation yet.

📋 Checklist:

• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "[vNext]" section of the CHANGELOG, linking to this pull request & included my GitHub handle to the release contributors list.

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[gasparnagy]

We need to rework this according to the final solution in reqnroll/Reqnroll#876 🙁

[clrudolphi]

Parking this; keeping it around temporarily for reference.
Going to break this into two parts: first one will do the generation (respecting the configured setting in reqnroll.json).
A second PR will provide a UI (if we ever decide such is needed).