Allow using nested C++ types of typedefs (GH-4039)

Closes https://github.com/cython/cython/issues/2233

Cython/Compiler/Nodes.py

@@ -1044,7 +1044,10 @@ class CSimpleBaseTypeNode(CBaseTypeNode):
                 scope = env
                 for item in self.module_path:
                     entry = scope.lookup(item)
-                    if entry is not None and entry.is_cpp_class:
+                    if entry is not None and (
+                        entry.is_cpp_class or
+                        entry.is_type and entry.type.is_cpp_class
+                    ):
                         scope = entry.type.scope
                     else:
                         scope = None

tests/run/cpp_nested_classes.pyx

@@ -26,6 +26,10 @@ cdef extern from "cpp_nested_classes_support.h":
         pass
 
 
+ctypedef A AliasA1
+ctypedef AliasA1 AliasA2
+
+
 def test_nested_classes():
     """
     >>> test_nested_classes()
@@ -47,6 +51,20 @@ def test_nested_typedef(py_x):
     cdef A.my_int x = py_x
     assert A.negate(x) == -py_x
 
+def test_typedef_for_nested(py_x):
+    """
+    >>> test_typedef_for_nested(5)
+    """
+    cdef AliasA1.my_int x = py_x
+    assert A.negate(x) == -py_x
+
+def test_typedef_for_nested_deep(py_x):
+    """
+    >>> test_typedef_for_nested_deep(5)
+    """
+    cdef AliasA2.my_int x = py_x
+    assert A.negate(x) == -py_x
+
 def test_typed_nested_typedef(x):
     """
     >>> test_typed_nested_typedef(4)