Implementation of KT-4288

Getters to access elements of indexed collections via rangers and iterators.

External functions implemented for:
List, Map, CharSequence, String, Array and primitive arrays (ByteArray, etc).

(cherry picked from commit b1f86f30edc5edc500d61c7c0230f5601029b2e7)

Conflicts:
	libraries/stdlib/src/kotlin/Strings.kt
improved the comments