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/diagnostics/tests/varargs/kt2163.kt

@@ -0,0 +1,7 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+fun printAll(vararg a : Any) {}
+
+fun main(args: Array<String>) {
+    printAll(*args) // Shouldn't be an error
+}