Improve decryption error UI by consolidating error messages and providing instructions when possible

[duxovni]

Reworked version of #8272, since that ended up on the back burner for several months.

Checklist

• Tests written for new code (and old code if feasible)
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

Screenshots

Display a spinner for a few seconds while we wait for keys to arrive

If this device isn't verified, and there are other devices or backups to verify against, tell the user to verify first

If this device isn't verified and there's nothing to verify with, tell the user to reset keys

If this device is verified and there are other verified devices, advise opening one of those

If this is the only verified device, there's not much to do

Bubble layout

Dark mode

---

Here's what your changelog entry will look like:

✨ Features

• Improve decryption error UI by consolidating error messages and providing instructions when possible (#9544). Contributed by @duxovni.

[richvdh]

@duxovni I've made a start on a review here, and made a bunch of comments. I've not looked at the test code at all yet.

Architecturally speaking, I find it very surprising to have the failure bar be responsible for sending out the room key requests, rather than that living elsewhere and the failure bar just being a view of what's going on. It may be that folks with more familiarity with E-W's architecture can either suggest better approaches or confirm that this this is a good approach.

Stylistically speaking:

• I'm surprised at the lack of comments here. I'm generally of the opinion that comments are important: not only do they explain to people reading/maintaining the code how it works, they can provide useful information on how the author expected things to work when there is a difference to reality. Without comments, the behaviour of functions and variables is left implicit, which means it's open to interpretation. TL;DR: more comments please.
• I am woefully out of touch with current React development practices. I may have made stupid suggestions, or missed obvious opportunities for improvement. Another pair of eyes would probably be beneficial.

Also, it looks like CI is currently failing on a number of fronts.

[duxovni]

I've added Jest tests for most of the interesting parts of this; the remainder is stuff that requires simulating an actual browser viewport and can't really be tested outside of Cypress, so the opinion from Web team chat was that it should be fine to override the SonarCloud gate in this case.