Search-on-views only works on view definitions with $addFields and/or $match in the definition. However, we currently don't have a test extension that desugars into only $addFields and/or $match.

Such an extension should actually fail search index CRUD operations as the server does not desugar extensions prior to sending a request to mongot. This means that even if an extension desugars into valid stages, the server should still see an invalid stage (the extension stage) and fail prior to sending a request to mongot. This PR should add an extension that desugars into valid stages and add to `search_index_view_validation.js` to verify that such a stage is caught by our view validation.