Restore RenderFunction, RenderFunctionSync, and RenderFunctionAsync

[karangattu]

Find the stack-trace below

E           RuntimeError: Shiny app exited without ever becoming ready. Waiting for 'Uvicorn running on' in stderr. Last 20 lines of stderr:
E               self.loaded_app = import_from_string(self.app)
E           
E             File "/Users/user/.pyenv/versions/3.10.12/lib/python3.10/site-packages/uvicorn/importer.py", line 24, in import_from_string
E           
E               raise exc from None
E           
E             File "/Users/user/.pyenv/versions/3.10.12/lib/python3.10/site-packages/uvicorn/importer.py", line 21, in import_from_string
E           
E               module = importlib.import_module(module_str)
E           
E             File "/Users/user/.pyenv/versions/3.10.12/lib/python3.10/importlib/__init__.py", line 126, in import_module
E           
E               return _bootstrap._gcd_import(name[level:], package, level)
E           
E             File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
E           
E             File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
E           
E             File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
E           
E             File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
E           
E             File "<frozen importlib._bootstrap_external>", line 883, in exec_module
E           
E             File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
E           
E             File "/Users/user/Documents/GitHub/py-shiny/shiny/api-examples/data_frame/app.py", line 4, in <module>
E           
E               from shinywidgets import output_widget, render_widget
E           
E             File "/Users/user/.pyenv/versions/3.10.12/lib/python3.10/site-packages/shinywidgets/__init__.py", line 8, in <module>
E           
E               from ._shinywidgets import output_widget, reactive_read, register_widget, render_widget, as_widget
E           
E             File "/Users/user/.pyenv/versions/3.10.12/lib/python3.10/site-packages/shinywidgets/_shinywidgets.py", line 33, in <module>
E           
E               from shiny.render import RenderFunction, RenderFunctionAsync
E           
E           ImportError: cannot import name 'RenderFunction' from 'shiny.render' (/Users/user/Documents/GitHub/py-shiny/shiny/render/__init__.py)

while running data_frame/app.py
Shinywidgets is importing RenderFunction and RenderFunctionAsync

[cpsievert]

This should get fixed as a part of posit-dev/py-shinywidgets#119

That said, I suppose this is problematic if folks upgrade shiny and not shinywidgets.

@schloerke how painful would it be to have better back-compat support? Also, I think we need to at least mention the removal of RenderFunction, RenderFunctionAsync as a breaking change?

[schloerke]

@cpsievert Yes, we'll need to put it back. I caught that with @karangattu last Friday.

[schloerke]

The classes will be hard deprecated in #1032, however the error message will be much clearer on how to move forward