Allow data classes to implement equals/hashCode/toString from base classes

#KT-11306 Fixed

compiler/testData/diagnostics/tests/dataClasses/implementMethodsFromInterface.kt

@@ -0,0 +1,25 @@
+// KT-11306 ABSTRACT_MEMBER_NOT_IMPLEMENTED for data class should inheriting interfaces requiring equals(), hashCode(), or toString()
+
+interface Foo {
+    override fun equals(other: Any?): Boolean
+    override fun hashCode(): Int
+    override fun toString(): String
+}
+
+data class FooImpl(val num: Int) : Foo
+
+data class FooImplSome(val num: Int) : Foo {
+    override fun hashCode() = 42
+}
+
+data class FooImplAll(val num: Int) : Foo {
+    override fun equals(other: Any?) = false
+    override fun hashCode() = 42
+    override fun toString() = "OK"
+}
+
+
+data class WrongSignatures(val num: Int) : Foo {
+    <!NOTHING_TO_OVERRIDE!>override<!> fun equals(other: WrongSignatures) = false
+    override fun hashCode(): <!RETURN_TYPE_MISMATCH_ON_OVERRIDE!>Boolean<!> = true
+}