Add toString() to Any, fix all tests

#KT-4517 Fixed

compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyDeclared.kt

@@ -1,5 +1,5 @@
 data class A(val x: Int) {
-  fun toString(): String = "!"
+  override fun toString(): String = "!"
 }
 
 fun box(): String {

compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyInherited.kt

@@ -1,5 +1,5 @@
 trait SuperTrait {
-    public fun toString(): String = "!"
+  override fun toString(): String = "!"
 }
 
 data class A(val x: Int): SuperTrait {

compiler/testData/codegen/boxWithStdlib/regressions/kt1800.kt

@@ -6,7 +6,7 @@ import java.util.ArrayList
 public class User(val firstName: String,
                   val lastName: String,
                   val age: Int) {
-    fun toString() = "$firstName $lastName, age $age"
+    override fun toString() = "$firstName $lastName, age $age"
 }
 
 public fun <T: Comparable<T>> Collection<T>.testMin(): T? {