This was a wasteful shortcut to MediaProxy.preview_url/1 and we don't
always want the preview_url in the metadata anyway.

This is what Mastodon uses and might fix some link preview bugs I've encountered

This brings them more in line with Mastodon.
- Deduplicates display name from the title and content
- Removes arbitrary limits on the size of the embedded image
- Removes angled double quotes from embed descriptions. These would normally just indicate that the content is a quote, but that is already implied by the content being in an embed.

grep -rl '# Copyright © .* Pleroma' * | xargs sed -i 's;Copyright © .* Pleroma .*;Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>;'

Gets rid of '|| ""' in multiple places and fixes #2067

Fix profile url for funkwhale channels, removes one source_data use

Closes #1653

See merge request !2333

Twitter cards were not passing any useful metadata. A few things were
being handled on Twitter's end by trying to match OpenGraph tags with
their own, but it wasn't working at all for media. This is an attempt to
fix that.

Common functions have been pulled out of opengraph and put into
utils. Twitter's functionality was entirely replaced with a direct copy
of Opengraph's and then modified as needed.

Profiles are now represented as Summary Cards

Posts with images are now represented as Summart with Large Image Cards

Posts with video and audio attachments are represented as Player Cards.

This now passes the Twitter Card Validator.

Validator and Docs are below

https://cards-dev.twitter.com/validator
https://developer.twitter.com/en/docs/tweets/optimize-with-cards/overview/abouts-cards