Regioselective Anionic [3+2] Cyclizations of Isoxazole, Pyrazole and 1,2,4‐Triazole Dinucleophiles − Efficient Synthesis of 2,4‐Dihydroimidazo[4,5‐b]quinoxalines, 3H‐Imidazo[1,2‐b]pyrazoles and 5H‐Imidazo[2,1‐c][1,2,4]triazoles