Add toString() to Any, fix all tests

#KT-4517 Fixed

core/builtins/native/jet/Any.kt

@@ -4,4 +4,6 @@ public open class Any {
     public open fun equals(other: Any?): Boolean
 
     public open fun hashCode(): Int
+
+    public open fun toString(): String
 }

core/builtins/native/jet/Library.kt

@@ -35,8 +35,6 @@ public trait CharSequence {
   public fun get(index : Int) : Char
 
   public val length : Int
-
-  public fun toString() : String
 }
 
 public class String() : Comparable<String>, CharSequence {
@@ -44,7 +42,6 @@ public class String() : Comparable<String>, CharSequence {
 
   public override fun compareTo(that : String) : Int
   public override fun get(index : Int) : Char
-  public override fun toString() : String
   public override val length: Int
 }