[mypyc] Fix calling a property that returns a callable

[rheard]

Fixes mypyc/mypyc#1212.

mypyc stores a property's getter as a method under the property's name, and gen_method_call checks for a method before it checks for an attribute. So obj.prop(x) on a native class was compiled as a direct call to the getter: x was dropped, and the call returned the property's value instead of calling it. For the example in the issue, the IR was:

r0 = config.sorting_function()
r1 = cast(list, r0)

This usually failed with a TypeError like the one in the issue (list object expected; got builtin_function_or_method). When the result type was object or Any (for example with Callable[[], object]), it silently returned the callable itself. super().prop(x) had the same problem in translate_super_method_call.

Now neither place treats a property getter as the method to call. obj.prop(x) calls the getter and then calls the value it returns, as mypyc already does for an attribute that holds a callable:

r0 = config.sorting_function
r1 = [to_sort]
r2 = load_address r1
r3 = PyObject_Vectorcall(r0, r2, 1, 0)
keep_alive to_sort
r4 = cast(list, r3)

super().prop(x) gets the value through super(), as super().prop already does..