Use `typing_extensions` instead of `inspect` and `typing` to correctly backport modern functionality

[ericbstie]

gqlrequests/query_creator.py suffers from whacky code that imports certain properties based on the current Python version. This makes mypy complain too, and per now these type errors are just ignored. The correct solution would be to use the typing_extensions module instead, which backports common type-related functions from inspect and typing.

https://typing-extensions.readthedocs.io/en/latest/