#993. More Struct tests added

LibTest/ffi/Struct/Struct_A06_t01.dart

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+/*
+ * Copyright (c) 2021, 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.
+ */
+/**
+ * @assertion Struct subclasses cannot be empty
+ *
+ * @description Checks that it is a compile error if Struct subclass is empty
+ * @author sgrekhov@unipro.ru
+ * @issue 44935
+ */
+import "dart:ffi";
+
+  class S1 extends Struct {
+//^^^^^^^^^^^^^^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  }
+
+void main() {
+  S1? s1;
+}

LibTest/ffi/Struct/Struct_A07_t01.dart

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+/*
+ * Copyright (c) 2021, 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.
+ */
+/**
+ * @assertion Struct cannot be implemented or used as a mixin
+ *
+ * @description Checks that it is a compile error if Struct is implemented
+ * @author sgrekhov@unipro.ru
+ * @issue 44935
+ */
+import "dart:ffi";
+
+class S1 implements Struct {
+//                  ^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+void main() {
+  S1? s1;
+}

LibTest/ffi/Struct/Struct_A07_t02.dart

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+/*
+ * Copyright (c) 2021, 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.
+ */
+/**
+ * @assertion Struct cannot be implemented or used as a mixin
+ *
+ * @description Checks that it is a compile error if Struct is used as a mixin
+ * @author sgrekhov@unipro.ru
+ * @issue 44935
+ */
+import "dart:ffi";
+
+class S1 extends Object with Struct {
+//                           ^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+void main() {
+  S1? s1;
+}