Update plugin to handle new style rules for virtual annotations.

tools/clang/plugins/tests/virtual_method_overannotated.cpp

+class Base {
+ public:
+  virtual void F1() = 0;
+  virtual void F2() = 0;
+  virtual void F3() = 0;
+};
+
+class Derived : public Base {
+ public:
+  // The three following lines should emit fix-it hints to remove the virtual.
+  virtual void F1() override {}
+  virtual void F2() final {}
+  virtual void F3() override final {}
+};