Avoid hoisting confusion, split code into separate snippets

Correcting "Default + Rest + Spread" examples to be 3 separate snippets, to avoid hoisting confusion (same function re-declared 3 times in same program).

Also, corrected * to + in second snippet, which makes `5` the correct result (`6` if it's `*`, but the other two snippets are `+`, so makes more sense to be consistent).