autorest produce conflicts when merging swagger

when PR deletes some swaggers, the breaking change pipeline will try merging all the swagger under the corresponding api-version folder which may produce conflicts

Start by tracing the breaking change pipeline and the logic that merges Swagger files under each api-version folder. Reproduce the case where a pull request deletes Swagger files, then verify that the pipeline no longer produces merge conflicts for the remaining specifications.

Written by the indexing model from the issue text.