[extractor/reddit] Support cookies and short URLs

[bashonly]

• Add support for shortened https://redd.it/{display_id} links, which redirect to a https://www.reddit.com/comments/{display_id} URL without a subreddit path

• Add support for cookies by removing old/broken quarantine-bypass method

• Add error handling for quarantined/private subreddits

Closes #6665, Closes #6753

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)