At two and a half hours, New York Revels' winter solstice fetedevoted, this year, to Scotland's artistrywas as overstuffed as a holiday goodies basket. Lovely singing and Highland flinging and storytelling and mumming stretched late into the day. A piper piped and a fiddler fiddled and the audience snaked around. On a stage festooned with evergreen, dozens of hearty performers offered instrumental pieces, poems, songs, and dances that flowed together seamlessly. A low-key gentleness prevailed, but one numberHalf Moon Sword's performance of the traditional Papa Stour Sword Dance of the Shetland Islandselectrified. Ten woman dancers presented themselves as soldiers with their long swords at the ready. With hilts and tips gripped in their fists, they formed a continuously moving chain whose increasingly complex rearrangements were rendered with the ease of wielding not a weapon but a silver needle and silken thread.