Use global constants for default arguments of cpdef functions/methods and def...

Use global constants for default arguments of cpdef functions/methods and def methods in cdef classes as using the CyFunction defaults requires passing the CyFunction as self (which we currently don't do for methods in cdef classes).
Properly fixing this requires changing the call signature of CyFunction.

Cython/Compiler/ExprNodes.py

@@ -8733,11 +8733,12 @@ class PyCFunctionNode(ExprNode, ModuleNameMixin):
         default_kwargs = []
         annotations = []
 
-        # For global cpdef functions and cpdef methods in cdef classes, we must use global constants
+        # For global cpdef functions and def/cpdef methods in cdef classes, we must use global constants
         # for default arguments to avoid the dependency on the CyFunction object as 'self' argument
         # in the underlying C function.  Basically, cpdef functions/methods are static C functions,
         # so their optional arguments must be static, too.
-        must_use_constants = self.def_node.is_wrapper and (env.is_c_class_scope or env.is_module_scope)
+        # TODO: change CyFunction implementation to pass both function object and owning object for method calls
+        must_use_constants = env.is_c_class_scope or (self.def_node.is_wrapper and env.is_module_scope)
 
         for arg in self.def_node.args:
             if arg.default and not must_use_constants: