KT-2397 Prohibit final methods in traits with no implementation

#KT-2397 fixed

compiler/testData/diagnostics/tests/declarationChecks/kt2397.kt

@@ -0,0 +1,17 @@
+//KT-2397 Prohibit final methods in traits with no implementation
+package a
+
+trait T {
+    <!FINAL_FUNCTION_WITH_NO_BODY!>final<!> fun foo()
+    <!FINAL_PROPERTY_IN_TRAIT!>final<!> val b : Int
+
+    final fun bar() {}
+    final val c : Int
+       get() = 42
+
+    final val d = <!PROPERTY_INITIALIZER_IN_TRAIT!>1<!>
+}
+
+class A {
+    <!NON_ABSTRACT_FUNCTION_WITH_NO_BODY!>final fun foo()<!>
+}