We are migrating towards using RTK Query for API calls, and using `msw`
to mock APIs in our tests.
RTK Query's `fetchBaseQuery` requires the use of `fetch` and `Request`.
`fetch()` was added to Node in v18, and the ability to use it in
Jest tests was added to Jest in v28. However, it still cannot be used
with a `jsdom` test environment.
Therefore, it is necessary to add a polyfill. There are several
libraries available for this but many others in this situation have had
success using `whatwg-fetch` and so it was selected somewhat
arbitrarily.
It is also important that `whatwg-fetch` is imported before
`fetchBaseQuery` (otherwise, a nuisance console warning will be issued).
To ensure this happens, it is imported in a Jest setup file.
