There is a growing need to validate the effects of generator changes, prior to having the changes checked in and released. This applies to both branded and unbranded generators. A regen preview pipeline should be created, similar to autorest's pipeline, so that we can test a change before releasing it.

As a nice to have, it would be helpful to have an option to choose between which generator to use, and also for cases where only a subset of libraries should be effected, it would be nice to select what libraries to regenerate.