Allow multiple definitions for operation with same name

For various reasons, I have a couple operations in my project that are duplicated that I don't want to/can't move to a single file and export. Because of this I end up getting the "multiple definitions for the operation" error until the extension eventually stops and I can't use it any more. Is there any interest in allowing multiple definitions, either by default or as a preference?

┆Issue is synchronized with this [Jira Task](https://apollographql.atlassian.net/browse/NEBULA-585) by [Unito](https://www.unito.io)

No files or tests are named. Start by locating the extension's validation path for the "multiple definitions for the operation" error, then determine how duplicate operations are discovered and whether preferences already govern validation. Done means duplicate definitions can be handled by the chosen default or preference without the extension becoming unusable.

Written by the indexing model from the issue text.