fixes #1395

[huumn]

• This refactors all plugins (gfm exempted) into a single rehype plugin
• It prevents making embeds out of links that has text sibling
• It prevents images/videos from inlining with its text siblings
• Begins moving some custom element component logic into non-rerendering rehype custom elements
• It collages adjacent images into a flex grid, whether
  • the images are all in the same p tag
  • the images are in independent p tags

The one failing of this improvement is that images/videos that aren't markeddown as images, ![](), won't collage. This can be fixed for proxied images by passing in imgproxyURLs to the plugin, but even without it seems like a fair trade.

QA: 6

TODO:

• should probably check code blocks, headings, and lists to make sure they still work.
• fix break of item/user hover popover
• refactor embeds
• refactor more of the component customization into the rehype plugin
• refactor text component into less of a mess
• refactor as much of the media-to-link component into the rehype plugin if possible
• refactor all sn remark and rehype plugins into a single rehype plugin
  • each tree visit or visitParents or findAndReplace walks every node in the tree

[huumn]

The ideal solution to this might be less heavy handed and create rehype plugins for embeds/media instead of treating them all as a.

[huumn]

I skipped the media-or-link refactor. The biggest mess of it all is the imgproxyURL handling. That should probably be moved to the server so it's typed and doesn't need to be unpacked in the view-related code.