Sync matrix users with contacts

### Your use case

#### What would you like to do?
I would like the ability to link matrix chat partners to entries in my system address book.

#### Why would you like to do it?
I have lots of contacts and find it hard to keep track a) what they are named, and what abilities to contact them I have. To centralise this information for almost all other forms of contact I use my address book, which a) keeps a list of identifiers this person is known under, and provides an authoritative name for that person system wide.

#### How would you like to achieve it?
I would like the ability to pair each chat partner to an address book entry in my system address book. This should a) allow me to click through from element to that address book entry, b) fetch the authoritative name for that person to display as the contact name and c) show the matrix handle of that person in the address book to allow link back from the address book to matrix.

### Have you considered any alternatives?

I can add the matrix entry manually to the address book, but that doesn't provide link back, and also matrix doesn't fetch the name from the address book. Also changes in the matrix name are not propagated to the address book.

### Additional context

I want this on my Mac, but it should also work on iOS.