Merge two static_final_field tests and rewrite a negative test to a multi-test

tests/language/static_final_field_negative_test.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-// Dart test program for testing static const fields.
-// This test should fail because fields a and c are static const fields
-// and they are missing initializers.
-
-class A {
-  const A() : n = 5;
-  final n;
-  static const a;
-  static const b = 3 + 5;
-  static const c;
-}
-
-class StaticFinalFieldNegativeTest {
-  static testMain() {
-    var a = new A();
-  }
-}
-
-main() {
-  StaticFinalFieldNegativeTest.testMain();
-}