Remove unnecessary `.trimEnd()` and fix facet detection (#3672)
* Fix link facet detection
Exclude the trailing period from the link, similar as done in the atproto package
* Fix JSON to text conversion
The trimEnd() call was only needed because we were always appending \n\n at the end. Fix that by only adding line breaks after non-final paragraphs.
* Detect paste reliably
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Co-authored-by: Dan Abramov <dan.abramov@gmail.com>
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