* Adding {% embed %} for liquid tags
This commit introduces the crease for us to unify our embed experience.
The main concept is introducing a lookup function for the given "link".
And with that lookup function find the underlying `LiquidTagBase` that
can handle the specific URL.
This is part proof of concept and part laying the foundation for a
plugin architecture of different LiquidTags.
We have a lot more work ahead of us to normalize this:
- Update and migrate existing data (not required but hopefully helps us
deprecate existing liquid tags)
- Move these "embeddable" tags into a module space that eases lookup.
- Document how someone might make a Railstie gem to inject new
embeddable formats into their application.
Related to #15099
* start adding UnifiedEmbeds to LiqTag models
* add specs for asciinema and codepen liqtags
* new tags and their specs
* complete first pass of liqtag models
* complete implementation for JsFiddleTag
* fixing twittertimeline tag
* almost done with YoutubeTag embed
* remove Medium UnifiedEmbed due to broken image in prod
* remove semi-working unified embed
* update specs
* Address PR review feedback
* add missing spec
* implement PR feedback
* last of PR review-related changes
* fix failing spec
Co-authored-by: Jeremy Friesen <jeremy.n.friesen@gmail.com>
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