Fixes https://github.com/cython/cython/issues/4243
(and probably a bunch more annotation bugs)

AnnotationNode doesn't have any child_attrs/subexprs because it mostly doesn't want to be analyzed (it's just transformed to an evaluable string). However this means that InterpretCompilerDirectives wasn't visiting its children to set is_cython_module and so the typing was failing. I've special-cased InterpretCompilerDirectives to visit AnnotationNode fully.