Massachusetts over the past 16 years has more than doubled the amount of tax breaks it provides businesses to spur economic development, but has only a vague idea whether the incentives are worthwhile, according to a new study by a Boston think tank. The Massachusetts Budget and Policy Center found that cost of the 58 “special business tax breaks” -- covering everything from making movies to selling aircraft parts -- has jumped to $770 million from $342 million in 1996.