Why suggestions for matirx ids?

[defini-tiv]

When you want to add a contact and start typing a matrix id, you will get suggestions for ids from people you dont know.

We should think about this behavior, because:

• you dont need this if know the id, if you don't you can use an identity server
• there is no (good) way of proving that this id belongs to the person you expect. So it can't be considerd useful for finding the id of people you wanted to find.
• its more beneficial for missuse, then for real use
• most other massangers dont do that
• most new people dont expect to be able to find others just by typing random names and find it wierd to possibly be found this way and take it as a sing for bad privacy.
• it would be beneficial for beeing considered as safe for underage (Play Store Age restriction element-android#4821) (although beeing able to find and join arbitrary rooms this way may be a bigger issue. But thats has at least areal usecase.)