* backend: support exporting Kotlin functions for C++ runtime
* runtime: implement several functions in Kotlin
* Throw{NullPointer,ArrayIndexOutOfBounds,ClassCast}Exception
* runtime: add literal declared in Kotlin as empty string
Also
* add corresponding test
* use empty string literal in strdedup2
(however keep it disabled)
* fixup! runtime: add literal declared in Kotlin as empty string
* Review feedback: add more TheEmptyString() usages
Also improve string index checks in runtime
Pavel Punegov