Meta report: https://meta.discourse.org/t/excessive-requests-to-uploads-lookup-urls-leading-to-429-response/143119
* The data-orig-src attribute was not being removed from cooked
video and audio so the composer was infinitely trying to get the
URLs for them, which would never resolve to anything
* Also the code that retrieved the short URL was unscoped, and was
getting everything on the page. if running from the composer we
now scope to the preview window
* Also fixed a minor issue where the element href for the video
and audio tags was not being set when the short URL was found
For consistency this PR introduces using custom markdown and short upload:// URLs for video and audio uploads, rather than just treating them as links and relying on the oneboxer. The markdown syntax for videos is  and for audio it is .
This is achieved in discourse-markdown-it by modifying the rules for images in mardown-it via md.renderer.rules.image. We return HTML instead of the token when we encounter audio or video after | and the preview renders that HTML. Also when uploading an audio or video file we insert the relevant markdown into the composer.
* DEV: Add API to alter uploads Markdown
* DEV: Extract data attributes from image / download Markdown
For example '[test|attachment|hello=world]' will generate an 'a' element
with a data attribute: 'data-hello=world'.
This commit also makes MarkdownIt to transform '|attachment' into
'class="attachment"'. This transformation used to be a part of the
process which resolves short URLs (i.e. upload://).
* DEV: Export imageNameFromFileName
* FIX: move attachment_css_class constant out of upload-short-url for discourse-markdown-it
* Use setTimeout instead of ember later
* WIP. Not sure if this worked.
* oneboxer cache in separate file
* Reset onebox cache still
* set functions for oneboxers cache
