WASHINGTON — Health officials urged the public Tuesday to prepare for the “inevitable” spread of the coronavirus within the United States, escalating warnings about a growing threat from the virus to Americans’ everyday lives.The urgent new tone from leaders of the federal Centers for Disease Control and Prevention and the National Institutes of Health came in response to a rapid surge in cases in new locations outside mainland China in the past several days, including new cases without a known source of exposure in Hong Kong, Iran, Italy, Japan, Singapore, South Korea, Taiwan and Thailand.