Arsenal have signed Brazil forward Gabriel Jesus from Manchester City for £45m on a long-term deal.   The 25-year-old is manager Mikel Arteta's fourth signing of the summer, following the arrivals of midfielder Fabio Vieira, goalkeeper Matt Turner and Brazilian striker Marquinhos   Arteta said he was "very excited" by Jesus' arrival.   "The club has done a tremendous job to recruit a player of this stature," he said.   Arteta, who worked with Jesus when an assistant coach at City, has been trying to boost Arsenal's attacking options following the departures of forwards Alexandre Lacazette and Pierre-Emerick Aubameyang