U.S. stock futures wobbled and oil dropped sharply Monday as investors grappled with the mounting economic toll after U.S. government officials signaled that measures to contain the coronavirus pandemic may remain in place for an extended time. Futures tied to the S&P 500 index wavered between gains and losses, suggesting that U.S. shares could be headed for another volatile trading session at the start of the week. U.S. crude-oil futures dropped to their lowest level in over 18 years, weighing on the shares of oil-and-gas…