Add common-types PATCH schema generation to typespec-autorest

- Add new decorator to designate Update common-types schema to typespec-autorest
- specify schema name and file placement
- Make it default behavior to reference common-types update schemas for PATCH requests in typespec-autorest
- Add config switch for generation of common-types update schema
- Add config switch to preserve current behaviors

Start by locating the typespec-autorest PATCH schema generation entry points, existing common-types handling, and configuration or decorator definitions. Determine how schema names and file placement are currently represented; done means the new decorator, default PATCH references, and both configuration switches are implemented without losing the current behavior.

Written by the indexing model from the issue text.