add support for calling named function variables

in _examples/funcs/test.py

```Python
# TODO: not currently supported:

# print("funcs.F1()...")
# f1 = funcs.F1()
# print("f1()= %s" % f1())
#
# print("funcs.F2()...")
# f2 = funcs.F2()
# print("f2()= %s" % f2())
#
# print("s1 = funcs.S1()...")
# s1 = funcs.S1()
# print("s1.F1 = funcs.F2()...")
# s1.F1 = funcs.F2()
# print("s1.F1() = %s" % s1.F1())
#
# print("s2 = funcs.S2()...")
# s2 = funcs.S2()
# print("s2.F1 = funcs.F1()...")
# s2.F1 = funcs.F1()
# print("s2.F1() = %s" % s2.F1())
```

I can't remember at this point what the issue(s) are but presumably there is nothing fundamental from preventing this from working.

从 _examples/funcs/test.py 开始，检查针对 funcs.F1、funcs.F2、funcs.S1 和 funcs.S2 的注释调用。运行该示例以确定其当前行为；当所示的具名函数变量调用可以启用并成功执行时，即表示完成。

由索引模型根据 Issue 内容生成。