Clear and concise description of the problem

During Brownfield conversion, it is important to have a combined swagger in order to do side by side comparison of conversion results.

Checklist

• Follow our Code of Conduct
• Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the TypeSpec repo
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.