Prior to this commit, unary operator spreading happened implicitly,
leading to surprises like typeof [] != typeof [0] (== [typeof 0]).
With this commit, a splat is required prior to the array being spread
over: typeof ...[0] == [typeof 0]. Implicit operator spreading is no
longer handled; typeof [0] is just typeof [0].

This enables ...[a, b] += 1 to have the same meaning as ++..[a, b].

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rhendric deleted the reform-operator-spread branch