Function toIterator

Converts most objects that can be an Iterator into one. The supported inputs are:

• An Iterator, will return the input as is/unchanged.
• An Iterable, will return the input with it's Symbol.iterator property called. So this includes any object that has a Symbol.iterator property. Like Arrays, Strings, Maps, Sets, etc.
• Any function with an optional sentinel argument, will return a FunctionIterator. This iterator will call the input func once per next() call and will stop once the value of sentinel (default: undefined) is returned from func.
• Any other non-nullable object, will return an ObjectIterator that iterates over the input object's own properties deeply.