Implement advanced iterator analysis

[lukastaegert]

Feature Use Case

Iterators can have side-effect but in many cases, e.g. when iterating arrays, they are side-effect free. This is a follow-up for #3126. Once this is implemented, for..of will always be penalized, which could be improved.

Feature Proposal

A sophisitcated solution could track Symbol.iterator and Symbol.asyncIterator properties and check the side-effects of their return values' next function. Such a logic should also work for spread operators and manual iteration as well as interact properly with generators. It should also be tested for side-effects when passed to a function such as Array.from.