Tokyo stocks opened higher Wednesday, encouraged by overnight gains on Wall Street and the yen’s slide the previous day to its lowest level against the U.S. dollar in over 20 years. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average rose 246.18 points, or 0.88 percent, from Tuesday to 28,190.13. The broader Topix index was up 17.02 points, or 0.87 percent, at 1,964.05. On the top-tier Prime Market, gainers were led by mining, real estate and machinery issues. At 9 a.m., the dollar fetched 132.82-83 yen compared with 132.59-69 yen in New York and 132.76-78 yen in Tokyo at 5 …