WASHINGTON — A $12 million Georgetown real-estate deal is putting another spotlight on one of the biggest shifts reshaping Washington: developers are increasingly looking at older commercial properties and seeing something the city badly needs more of — housing. Douglas Development Corp. has sold the mixed-use building at 2715 M Street NW to Adams Investment Group for $12 million, with plans for the property to become a high-end residential development. The roughly 29,000-squ