The shell escape function is now using `""` instead of `\"`. `utils.Popen` has been patched to properly quote commands.
Prior to this fix using `--exec` together with `%q` when on Windows could cause remote code to execute. See https://github.com/yt-dlp/yt-dlp/security/advisories/GHSA-42h4-v29r-42qg for reference.
Authored by: Grub4K
Using https://github.com/asottile/pyupgrade
1. `__future__` imports and `coding: utf-8` were removed
2. Files were rewritten with `pyupgrade --py36-plus --keep-percent-format`
3. f-strings were cherry-picked from `pyupgrade --py36-plus`
Extractors are left untouched (except removing header) to avoid unnecessary merge conflicts
