Improve rageshake upload experience by providing useful error information

[Half-Shot]

Fixes the Element Web side of element-hq/element-meta#2732

This makes a few changes:

• The rageshake API now uses fetch (as we have to be conditional about the response type, anyway).
• We now support Report error responses as JSON matrix-org/rageshake#90, with sensible fallbacks for the old API.
• The rageshake dialog now shows a translatable error where possible for the failure, falling back to the server provided one.

Previews

For a known errorcode

For a unknown errorcode

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.
• [N/A] I have licensed the changes to Element by completing the Contributor License Agreement (CLA)

[t3chguy]

Reusing the i18n key will be confusing here for other languages as the meaning has drastically changed. Also doesn't this fit within "causes"? e.g. cause=unreachable

[Half-Shot]

I think we don't actually need to change this now there is sufficient coverage via failed_send_logs_causes for errors returned by the API. For everything else, I think this error is fine.

[t3chguy]

The previous string (which will be what all other languages use for the foreseeable) is a partial sentence, ending with a colon. It'll never have any text rendered after it again, it'll look broken. It still needs a new key

[Half-Shot]

Okay, round 3 (4?). Tried to tidy this up.

[Half-Shot]

Will merge once matrix-org/rageshake#90 has landed.

[Half-Shot]

(seemed like a random test flake to me)