[lib][native][web] Extend findUserIdentities response type

Summary:
Updated Flow types and validators to include extended response of the FindUserIdentities RPC.
Kept previous logic, I didn't made any use of the new extended response.

Depends on D12925

Test Plan: Flow, repeated test plan from D12925 (generally played with modified functions). Made sure they work as before

Reviewers: ashoat, inka

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D12926