They’re not dissing Third Avenue anymore. Reflecting the corridor’s rising fortunes after years of “Third’s the Bird” jokes, the redevelopment of 850 Third has added a tasty side dish to its $80 million menu of inside-and-out repositioning.  Waterman Interests and HPS Investment Partners, owners of the mostly vacant, 605,000 square-foot Midcentury tower between East 51st and 52nd streets, signed a big-league restaurant even as work continues apace to re-launch the refreshed property by the end