Move comparison related functions to kotlin.comparisons, update imports in stdlib.

libraries/stdlib/test/OrderingTest.kt

@@ -3,6 +3,7 @@ package test.compare
 import java.util.*
 import kotlin.test.*
 import org.junit.Test
+import kotlin.comparisons.*
 
 data class Item(val name: String, val rating: Int) : Comparable<Item> {
     public override fun compareTo(other: Item): Int {