Governors Island, a treasure 800 yards from the coast of Manhattan and only 400 yards from Brooklyn, has opened for the 2018 season with something to interest, beguile and amaze just about anyone. For starters, there’s the island itself, with its forts and other historical monuments, its shaded, grassy lawns, its vistas of the harbor, its sea and land birds, its wildflowers and its hills where a soft wind blows even when city streets are sticky and hot.