Made vararg parameters have Array<out T> type

instead of simply Array<T>
  #KT-1638 Fixed
  #KT-2163 Fixed
  #KT-3213 Fixed
  #KT-4172 Fixed
  #KT-5534 Fixed

compiler/testData/codegen/box/vararg/kt796_797.kt

@@ -1,5 +1,5 @@
 fun <T> Array<T>?.get(i : Int?) = this!!.get(i!!)
-fun <T> array(vararg t : T) : Array<T> = t
+fun <T> array(vararg t : T) : Array<T> = t as Array<T>
 
 fun box() : String {
     val a : Array<String>? = array<String>("Str", "Str2")