"Glamour is something you can't bear to be without once you're used to it."                                                                                                                 -Loretta Young   Stretched across three exposures of The Dorchester, high above the city's frenetic din, a soign  e sanctuary beckons. The most desirable of the building's combined layouts, this airy abode is dappled in light and glamour. (Of course it is.) This exquisite residence is the New York home of legendary actress Joan Collins.   Beyond the entrance gallery, a sweeping openness enlivens the space, where the living and dining rooms meet across an expanse of windows. Three grand bedrooms enjoy an abundance of storage, and each is contiguous to a full bath. A floorplan this vast invites extraordinary possibilities.  Located on 57th Street at Park Avenue, The Dorchester is situated at the world's crossroads of culture, fashion, and commerce. This venerable white-glove co-op offers a full-time doorman, concierge, laundry facilities, housekeeping services, and an on-site garage. Characteristic of its peerless reputation for accommodation, the building welcomes pets and pieds-  -terre.