From galleries to tea dances, this waterfront stretch defines Ptown’s ever-evolving identity.Riding bikes along Commercial Street in Provincetown.Credit: Getty ImagesBefore the Mayflower landed at Plymouth Rock, it paused in the harbor of what would become Provincetown, Massachusetts (“to drop off the drag queens,” locals like to say with a wink). The Pilgrims spent several weeks here in 1620—long enough to agree on both the Mayflower Compact an…