Display a warning when an unverified user's identity changes

[uhoreg]

Fixes https://github.com/element-hq/element-meta/issues/2513

Checklist

• [ ] Tests written for new code (and old code if feasible).
• [ ] New or updated public/exported symbols have accurate TSDoc documentation.
• [ ] Linter and other CI checks pass.
• [ ] I have licensed the changes to Element by completing the Contributor License Agreement (CLA)

[CLAassistant]

All committers have signed the CLA.

[uhoreg]

I think that I've addressed all of @florianduros 's concerns. The test failure looks like possible flakiness, since it's testing components that I haven't touched.

[uhoreg]

@florianduros I've made the changes that you've requested to the test file. I'm afraid that I don't quite understand what you're asking for regarding pulling things out into custom hooks. I tried finding a natural division of the hooks to pull out together, but they're so interconnected, I would end up either creating a custom hook that just contained everything (which doesn't seem any better than what's currently there), or else, I would have hooks that would have a ton of arguments (which seems ugly to me). Could you give me a better idea of what you were thinking of?

[uhoreg]

@florianduros ping

[uhoreg]

I've addressed all of Florian's concerns. @richvdh can you give this a crypto team review?

[uhoreg]

I managed to find another race condition while writing a test, so I need to investigate and fix it.

[uhoreg]

Strange. One of the tests is now failing in CI, even though I only made a comment change. And I can't reproduce the failure locally. Will need to investigate.