Invite dialog: display MXID on its own line

[AndrewFerr]

The reason for doing this is to make the invite dialog more readable when the inviter's MXID is very long, which tends to be the case when the inviter is a bridged user with a machine-generated MXID.

Screenshots

DM invite

Before

After

Room invite

Before

After

Checklist

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

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Here's what your changelog entry will look like:

✨ Features

• Invite dialog: display MXID on its own line (#11756). Contributed by @AndrewFerr.