Add type hints to HttpResponse

[michelole]

It seems HttpResponse is the only class in this file that does not contain type hints.

This generates errors when client code is checked using mypy in strict mode:

error: Call to untyped function "HttpResponse" in typed context

Add type hints following the docstring.

[vrdmr]

@tonybaloney - I think this change will need a corresponding change in _http_asgi.py to fix the type annotations for the headers in to_func_response.

=================================== FAILURES ===================================
__________________________ TestCodeQuality.test_mypy ___________________________
Traceback (most recent call last):
  File "/home/runner/work/azure-functions-python-library/azure-functions-python-library/tests/test_code_quality.py", line 32, in test_mypy
    f'mypy validation failed:\n{output}') from None
AssertionError: mypy validation failed:
azure/functions/_http_asgi.py:73: error: Argument "headers" to "HttpResponse" has incompatible type "Union[Headers, Dict[Any, Any]]"; expected "Optional[Mapping[str, str]]"
Found 1 error in 1 file (checked 45 source files)

[ghost]

All CLA requirements met.

[michelole]

@vrdmr @tonybaloney I have ignored the error for the moment following similar code in _http_wsgi.py.

A proper solution would be to make a consistent usage of the Headers class in HttpResponse, thus deprecating HttpResponseHeaders and BaseHeaders, which are only used there and do not seem to support duplicate keys. I believe that should be tackled in a different issue/PR though.

[michelole]

@vrdmr @gavin-aguiar Any updates here? Since the mypy error was fixed, could we remove the "Blocked" label?

[michelole]

@AnatoliB @anirudhgarg @gavin-aguiar Could you have a look on this PR as required reviewers?

Ps.: @vrdmr It seems tests are failing/cancelling across all builds and are not related to this PR only.

[vrdmr]

LGTM.

[vrdmr]

Thanks a lot, @michelole for the contribution, and apologies for the delay.

I'll fix the CI issues with our workflow caused due to a PR coming from a fork. Thanks again.