Given a method, which may come from an interface, and a targetClass used
in the current AOP invocation, find the most specific method if there is
one. E.g. the method may be IFoo.bar() and the target class may be
DefaultFoo. In this case, the method may be DefaultFoo.bar(). This
enables attributes on that method to be found.
method - method to be invoked, which may come from an interface
targetClass - target class for the current invocation. May be
null or may not even implement the method.
the more specific method, or the original method if the
targetClass doesn't specialize it or implement it or is null