If the collection of elements to be added is empty, java6 implementation
of AbstractMutableList.addAll doesn't throw on invalid index.
The failing test was introduced in 59031543e2
which fixed #KT-47211.
- Int.toChar was left non-deprecated because the replacement is not intrinsic yet.
- Number.toChar was left non-deprecated because otherwise the deprecation propagates to the override, Int.toChar.
KT-23451