MSW: migrate login handlers

[deer-wmde]

continuation of #1114

contains some fixes to the prior work and adjustments to the current codebase

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This patch starts the migration from the broken 1.x MSW configuration to a 2.x one.

It adjusts our browser mocks to use the new msw/browser using the Fetch API (https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API).

In the new handlers it moves over just login functionality as well as the querying for user wikis and missing policies, leaving the remaining handler migration to future work.

Co-authored-by: rosalieper 15235452+rosalieper@users.noreply.github.com
Co-authored-by: outdooracorn 43674967+outdooracorn@users.noreply.github.com
Co-authored-by: tarrow 7353563+tarrow@users.noreply.github.com

https://phabricator.wikimedia.org/T436360

[github-actions]

Deployment previews on netlify for branch refs/pull/1184/merge will be at the following locations (when build is done):

• UI with mock store: https://57789d4185-mock--wbstack-ui.netlify.app/
• UI pointing to prod: https://57789d4185-prod--wbstack-ui.netlify.app/

[dati18]

I think you did a good job on this. But I want to point out a few inconsistencies (a bit nitpicking)

MSW v2 has HttpResponse helpers, and I believe it was designed around them. For example:

• HttpResponse.json()
• new HttpResponse(null, { status: 204 })

Official v2 doc: https://mswjs.io/docs/api/http

[deer-wmde]

I think you did a good job on this. But I want to point out a few inconsistencies (a bit nitpicking)

MSW v2 has HttpResponse helpers, and I believe it was designed around them. For example:

* `HttpResponse.json()`

* `new HttpResponse(null, { status: 204 })`

Official v2 doc: https://mswjs.io/docs/api/http

Thanks! Yes, I'm aware of the msw's HttpResponse - I went with the Response the standard API implementation (docs) because I didn't see much worth yet of using theirs: currently the docs mention mostly cookie response mocking (which I think we are still able to do as seen in this PR) and some shorthand methods. Given this refactoring was mostly needed because previously they used some custom implementation I thought it'd be a good call to stick to standards as close as possible, even if their extension is minimal so far and they pinky promise that it stays that way. Still I could be convinced to use it instead if devs prefer it. Good thing to bring up, thanks!

[rosalieper]

Looks good to me !!!