The recent announcement that Mattel and the producers of “Baywatch”have joined forces to create Baywatch Barbie came as no surprise.After all, both companies have made millions off airheads withflawless skins, Malibu tans, and synthetic breasts.If Baywatch Barbie sells well, other Barbie/TV tie-ins seem certainto follow. Some possibilities:Melrose Place Barbie: Comes