It’s crowded in the back of the ambulance.Two emergency medical technicians, the patient, the gurney — and an unseen and unwelcome passenger lurking in the air.For EMTs Thomas Hoang and Joshua Hammond, the coronavirus is constantly close. COVID-19 has become their biggest fear during 24-hour shifts in California’s Orange County, riding with them from 911 call to 911 call, from patient to patient.They and other