It should be possible to link Matrix IDs to the address book / contacts

### Your use case

#### What would you like to do?

This already has been requested for Element almost four years ago: https://github.com/element-hq/element-android/issues/1708 – it would be nice if somehow, one could link Matrix IDs to the contacts, so that e.g. the saved name shows up in chats instead of the (sometimes odd) profile name of the respective Matrix ID.

#### Why would you like to do it?

This would lead to better integration, allow custom display names for the people we chat with (e.g. "Mom" instead of the real name mom could have set as the profile name), and be in line with what other messengers do – and what people most likely expect from a messenger.

#### How would you like to achieve it?

I'm not into Android development enough to be able to propose how to do it. Maybe through some custom "Matrix ID" field? Or maybe, contacts could be identified via their email address?

### Have you considered any alternatives?

I don't think there are alternatives. Setting a display name would be unnecessary overhead and it would not solve the root problem.

### Additional context

_No response_

### Are you willing to provide a PR?

No

No source file, test, or entry point is named. Start by investigating how Element X represents contacts, Matrix IDs, and display names, then review the linked Element Android issue for prior context. Done would require an agreed design for linking Matrix IDs to contacts and clear acceptance criteria for the displayed contact name.

Written by the indexing model from the issue text.