Start new chat via Contacts Book: Ask if user wants to share phone number

[peter-czy]

It would be a huge step towards a real competitive mass-messenger if element asked the user for sharing the phone number when he/she tries to find chat partners via Contacts Book (in DM Tab click on FAB to start new chat - "Contacts Book").

Currently, element asks for permission to read your contacts book but will probably find no contacts because 'normal' users don't register their number (since this is not being asked in the registration flow and is only in settings where 'normal' users don't look right at the beginning).

Instead, the user should be asked before (!) showing possible chat partners based on their shared contacts to enter his/her number. This will significantly increase the the number of people who will be found on matrix via phone number.