KT-2819 Duplicate toString() method generated in data class

#KT-2819 Fixed

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

@@ -0,0 +1,7 @@
+data class A(val x: Int) {
+  fun toString(): String = "!"
+}
+
+fun box(): String {
+  return if (A(0).toString() == "!") "OK" else "fail"
+}

compiler/testData/codegen/dataClasses/tostring/alreadyDeclaredWrongSignature.kt

@@ -0,0 +1,17 @@
+data class A(val x: Int) {
+  fun toString(other: Any): String = ""
+}
+
+data class B(val x: Int) {
+  fun toString(other: B, another: Any): String = ""
+}
+
+fun box(): String {
+  javaClass<A>().getDeclaredMethod("toString")
+  javaClass<A>().getDeclaredMethod("toString", javaClass<Any>())
+
+  javaClass<B>().getDeclaredMethod("toString")
+  javaClass<B>().getDeclaredMethod("toString", javaClass<B>(), javaClass<Any>())
+
+  return "OK"
+}