National drugstore chains, once resistant to the retail apocalypse that swept across the U.S., are finally succumbing to competition from online shopping and discount stores. About 3,000 fewer drugstores were open for business at the start of this year compared with the same period in 2019, according to analytics company RetailStat, which tracks 15 pharmacy chains.  CVS Health, Walgreens and Rite Aid have each closed hundreds of stores since the onset of the...