add a wrap_decorator decorator to keep the __doc__ attr

[SigureMo]

PR types

Bug fixes

PR changes

Others

Describe

try to fix the missing docstring of paddle.jit.save, the details describe in PaddlePaddle/docs#5243 (comment)

目前通过 paddle.jit.save.__doc__ 无法获取到 docstring，原因是装饰器没有传递内层函数的 __doc__ 属性

Paddle/python/paddle/fluid/dygraph/jit.py

Lines 682 to 687 in fd56f08

	@_run_save_pre_hooks
	@switch_to_static_graph
	def save(layer, path, input_spec=None, **configs):
	"""
	Saves input Layer or function as ``paddle.jit.TranslatedLayer``
	format model, which can be used for inference or fine-tuning after loading.

其中 switch_to_static_graph 已经使用 wrap_decorator 装饰过，因此不会造成 __doc__ 等属性的丢失，而 _run_save_pre_hooks 没有，因此使用 wrap_decorator 装饰下，尝试下效果

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[SigureMo]

本地编译 wheels 安装测试，修改前后的效果如下：

	before	after
Jupyter Notebook
REPL help function
__doc__ attribute

[chenwhql]

LGTM

[jzhang533]

LGTM