WASHINGTON — Spending on veterans’ health care could double in three years under the Senate’s solution to the long waits experienced by thousands seeking medical care at VA hospitals and clinics, according to congressional budget experts. Analyzing a bill the Senate passed overwhelmingly last Wednesday, the Congressional Budget Office estimates the measure would add $35 billion over the next three years to the $44 billion the government now spends annually on medical care for veterans. Both the Senate bill and a House version also passed this past week would dramatically expand government-paid health care.