[reddit] support images and videos inside text posts

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Images and videos can be embedded inside text posts using the fancy-pants editor in New Reddit, which gallery-dl does not pick up. Their format seems to be \n\n<p><a href="image url">caption or url again</a></p>\n. Some test posts I wrote and information I gathered about them:

In https://reddit.com/r/test/comments/wkzf4i/is_media_metadata_sorted_by_something_else (old reddit, json): Images that are uploaded to the post are in media_metadata while links that look like images are not. media_metadata seems to be sorted in alphabetical order of its keys however, so we'd probably need to parse the text.

In https://reddit.com/r/test/comments/wl01st/more_testing (old reddit, json): There are links to images that are in the post which could be parsed as images (but I had to send HTTP requests to add them in since the editor kept bugging out, so this probably is a nitpick or non-issue). I've MITM'd New Reddit and saw that adding &rtj=1 to the url lets you get another representation of the post's body that lets you distinguish between images and links.

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I'm willing to implement this, but should &rtj=1 be used?

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What should be done if extractor.reddit.videos is set to ytdl? youtube-dl and yt-dlp currently don't support these posts either, nor do I really plan to make them (unless if necessary)