nextIndex
 Platform and version requirements: JVM (1.0), JS (1.1), Native (1.3) 
abstract fun nextIndex(): Int
Returns the index of the element that would be returned by a subsequent call to next.
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Licensed under the Apache License, Version 2.0.
    https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-list-iterator/next-index.html