[Bug]: Remove unnecessary 'type-extensions' requirement

[danphenderson]

I am using the latest version. This is more of a code smell than a bug.

Context

The setup.py specifies type-extensions as an unnecessary requirement when installing the library into a Python 3.8 environment.

The type-extensions package is referenced in various places as:

import sys
from typing import Any, Dict, List, Optional, Sequence, Union

if sys.version_info >= (3, 8):  # pragma: no cover
    from typing import Literal, TypedDict
else:  # pragma: no cover
    from typing_extensions import Literal, TypedDict

Note, sys.version_info >= (3, 8) is always True since playwright only supports versions >=3.8. Consequently, the else block is never executed. Additionally, Literal and TypeDict were introduced into the standard typing module in 3.8 and 3.6, respectively, and a patch should access them from typing.

Environment

- Operating System: macOS
- CPU: [arm64]
- Browser: [All, Chromium, Firefox, WebKit]
- Python Version: [3.9]
- Other info: N/A