swift codegen - fragments not included in queries in operation IDs JSON

**Intended outcome:**

When generating a manifest of operation IDs / queries via the `--operationIdsPath` option, the JSON file should include fragment definitions.

**Actual outcome:**

Fragment definitions are missing from the queries.

**How to reproduce the issue:**

See repo here (codegen command used is in `package.json`): https://github.com/darrenclark/apollo-operation-ids-issue

Diff with a fixed copy of the JSON file: https://github.com/darrenclark/apollo-operation-ids-issue/compare/fixed

**Versions**

2.16

Start with the codegen command in the linked reproduction's package.json and inspect the --operationIdsPath output, using the linked fixed JSON diff as the expected result. Trace how fragment definitions are collected for Swift codegen; done means the generated operation-IDs JSON includes the required fragment definitions in its queries.

Written by the indexing model from the issue text.