Render M_SAFETY errors (MSC4387)

[Half-Shot]

Requires #31523
Requires matrix-org/matrix-js-sdk#5107
Uses MSC4387

Renders the new MSC4387 safety errors where we would usually render generic message failed to send errors, the specifics are:

• We can now show you the precise rule / harm you are violating,
• Some messages can be retried, others cannot (and must be deleted).

Reviewer notes:

• I'd like to get sign off from @element-hq/trust-safety before it goes through Element Web review, unfortunately GitHub lacks the nuance to handle that :)
• This is missing unit tests, @Half-Shot needs to fix that.

Checklist

• I have read through review guidelines and CONTRIBUTING.md.
• 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)

[t3chguy]

Given this isn't in labs it'll want design/product sign-off

[jimmackenzie]

Minor tweaks to the error content.

[jimmackenzie]

Is OurServerreplaced with the server name via text interpolation? If not, we should reword this:

This content is not permitted perhaps?

[Half-Shot]

This is just the error the server is returning. I think the MSC says that if the harm isn't known, we should defer to the server's message?

[t3chguy]

I think the MSC says that if the harm isn't known, we should defer to the server's message?

We shouldn't be showing untranslated server errors ever, this violates some customer commitments we have to be fully i18nable

[Half-Shot]

Noted, I'll leave feedback on the MSC. It doesn't appear to be a must so we can use generic wording for this.

[turt2live]

deferring strings review to Jim as the more qualified person :)