Introduced CompositeExtension (to pass several of them).
Disallowed using type parameter as reified type argument.

 #KT-3050 fixed
Removed toArray() from collections (few tests are still failing).

 #KT-3352 in progress
Generated default implementations for Collection.toArray().

 #KT-3352 in progress
Added copyToArray intrinsic method.

 #KT-3352 fixed