Wanted: Ability to force-export fragments in generatedTypes

In our codebase `generatedTypes.ts` includes some useful fragments that are not being exported. I believe these are fragments that aren't defined manually in a `.gql` file and are auto-generated based on other fragment definitions, specifically some that use
`... on SomethingElse`
in their body, resulting in non-exported fragments like `Something_SomethingElse_Fragment`.

It would be really cool if there was a way to force `codegen` to export these as well.

Start by tracing the codegen path that produces generatedTypes.ts and inspect how fragments containing `... on SomethingElse` are classified for export. The work is done when there is a supported way to force those generated fragments, such as `Something_SomethingElse_Fragment`, to be exported.

Written by the indexing model from the issue text.