[FeatureRequest] Support Python 3.9 style hinting using standard collections per PEP 585

[drewsilcock]

The worker supports Python 3.9, however does not work with type hinting using standard collections as specified in PEP 585 and introduced in Python 3.9.

Pre-PEP 585 style typing, which works:

from typing import List

# `func host start` is happy with this style of type hinting.
def main(events: List[func.EventHubEvent]) -> None:
    ...

New PEP 585 style typing, which doesn't work:

# `func host start` produces error here.
def main(events: list[func.EventHubEvent]) -> None:
    ...

The error produced is:

Worker failed to load function: 'my_function_name' with function id: '12345678-9012-3456-7890-abcdef123456'.
[2022-05-17T08:58:41.245Z] Result: Failure
[2022-05-17T08:58:41.245Z] Exception: TypeError: issubclass() arg 1 must be a class
[2022-05-17T08:58:41.245Z] Stack:   File "/opt/homebrew/Cellar/azure-functions-core-tools@4/4.0.4483/workers/python/3.9/OSX/X64/azure_functions_worker/dispatcher.py", line 311, in _handle__function_load_request
[2022-05-17T08:58:41.245Z]     self._functions.add_function(
[2022-05-17T08:58:41.245Z]   File "/opt/homebrew/Cellar/azure-functions-core-tools@4/4.0.4483/workers/python/3.9/OSX/X64/azure_functions_worker/functions.py", line 204, in add_function
[2022-05-17T08:58:41.245Z]     checks_out = bindings.check_input_type_annotation(
[2022-05-17T08:58:41.245Z]   File "/opt/homebrew/Cellar/azure-functions-core-tools@4/4.0.4483/workers/python/3.9/OSX/X64/azure_functions_worker/bindings/meta.py", line 44, in check_input_type_annotation
[2022-05-17T08:58:41.245Z]     return binding.check_input_type_annotation(pytype)
[2022-05-17T08:58:41.245Z]   File "/opt/homebrew/Cellar/azure-functions-core-tools@4/4.0.4483/workers/python/3.9/OSX/X64/azure/functions/eventhub.py", line 20, in check_input_type_annotation
[2022-05-17T08:58:41.245Z]     or (isinstance(pytype, type) and issubclass(pytype, valid_types))
[2022-05-17T08:58:41.245Z]   File "/opt/homebrew/Cellar/[email protected]/3.9.12/Frameworks/Python.framework/Versions/3.9/lib/python3.9/abc.py", line 123, in __subclasscheck__
[2022-05-17T08:58:41.245Z]     return _abc_subclasscheck(cls, subclass)

System info, in case it's relevant:

• OS - macOS Monterey 12.3.1
• func --version - 4.0.4483
• python --version - Python 3.9.12