PORTLAND, Ore.—Some 5,000 hospital health care workers walked off the job Friday as they picketed all eight Providence hospitals in Oregon, in what the state health workers union described as the largest health care strike in Oregon history—and the first to involve doctors. Most of those participating in the open-ended strike are nurses. But in a rare move, dozens of doctors at a Portland hospital and at six women’s health clinics are also partaking, making it the state’s first physicians strike, according to the Oregon Nurses Association union. The strike came after more than a year of negotiations failed to produce an agreement over staffing levels, pay and benefits….