Add support for parsing C++11 final classes

Such as:

  class X final {};

This no longer gives a syntax error.
This change has introduced one more shift-reduce conflict in the parser.
with a conflict with a C style variable declaration with name final:

  class X final;

resulting in a syntax error (for C++ not C). This is an an unusual style
for C++ code and more typical declarations do work:

  X final;

Closes #672

Doc/Manual/CPlusPlus11.html

@@ -891,6 +891,19 @@ struct DerivedStruct : BaseStruct {
 };
 </pre></div>
 
+<p>
+Classes can also be marked as final, such as
+</p>
+
+<div class="code"><pre>
+struct FinalDerivedStruct final : BaseStruct {
+  virtual void ab() const override;
+};
+</pre></div>
+
+<p>
+<b>Compatibility note:</b> Final methods were supported much earlier than final classes. SWIG-4.1.0 was the first version to support classes marked as final.
+</p>
 
 <H3><a name="CPlusPlus11_null_pointer_constant">7.2.12 Null pointer constant</a></H3>