Incrroect encoding when python read file
https://github.com/Dav1dde/glad/blob/1ecd45775d96f35170458e6b148eb0708967e402/glad/files/__init__.py#L22-L31

If `resource_exists` failed, script will use `open` to read file, but local host encoding. So I got the error:

```
UnicodeDecodeError: 'gbk' codec can't decode byte 0xbf in position 2: illegal multibyte sequence
```

Here are some of my suggestions.

- It's not recommended to use `pkg_resources`.

https://setuptools.pypa.io/en/latest/pkg_resources.html
> Use of pkg_resources is deprecated in favor of importlib.resources, importlib.metadata and their backports (importlib_resources, importlib_metadata). Some useful APIs are also provided by packaging (e.g. requirements and version parsing). Users should refrain from new usage of pkg_resources and should work to port to importlib-based solutions.

- Use `PYTHONWARNDEFAULTENCODING=1` to fix potential encoding errors.