Rename Stream<T> to Sequence<T> and provide migration path via deprecated types and functions.

libraries/stdlib/test/collections/MutableCollectionsTest.kt

@@ -21,7 +21,7 @@ class MutableCollectionTest {
         val list = listOf("foo", "bar")
         val collection = ArrayList<String>()
 
-        collection.addAll(list.stream())
+        collection.addAll(list.sequence())
 
         assertEquals(list, collection)
     }