Add a test ensuring mutable map preserves iteration order after update

libraries/stdlib/test/collections/MapTest.kt

@@ -309,7 +309,8 @@ class MapTest {
     @Test fun createMutableMap() {
         val map = mutableMapOf("b" to 1, "c" to 2)
         map.put("a", 3)
-        assertEquals(listOf("b" to 1, "c" to 2, "a" to 3), map.toList())
+        map["b"] = 0
+        assertEquals(listOf("b" to 0, "c" to 2, "a" to 3), map.toList())
     }
 
     @Test fun createLinkedMap() {