Data classes cannot have class supertypes, a new test, relevant test fixes

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

@@ -0,0 +1,11 @@
+interface Allowed
+
+open class NotAllowed
+
+abstract data class Base(val x: Int)
+
+class Derived: Base(42)
+
+<!DATA_CLASS_OVERRIDE_CONFLICT!>data<!> class Nasty(x: Int, val y: Int): <!DATA_CLASS_CANNOT_HAVE_CLASS_SUPERTYPES!>Base<!>(x)
+
+data class Complex(val y: Int): Allowed, <!DATA_CLASS_CANNOT_HAVE_CLASS_SUPERTYPES!>NotAllowed<!>()