Twitter does not allow SVGs to be used for twitter:image
metadata (see https://developer.twitter.com/en/docs/twitter-for-websites/cards/overview/markup)
so we should fall back to the site logo if the image option
provided to `crawlable_meta_data` or SiteSetting.site_twitter_summary_large_image_url
is an SVG, and do not add the meta tag for twitter:image at all
if the site logo is an SVG.
Instead of using image-uploader, which relies on the old
UploadMixin, we can now use the uppy-image-uploader which
uses the new UppyUploadMixin which is stable enough and
supports both regular XHR uploads and direct S3 uploads,
controlled by a site setting (default to XHR).
At some point it may make sense to rename uppy-image-uploader
back to image-uploader, once we have gone through plugins
etc. and given a bit of deprecation time period.
This commit also fixes `for_private_message`, `for_site_setting`,
and `pasted` flags not being sent via uppy uploads onto the
UploadCreator, both via regular XHR uploads and also through
external/multipart uploads.
The uploaders changed are:
* site setting images
* badge images
* category logo
* category background
* group flair
* profile background
* profile card background
Jarek Radosz
Martin Brennan
Martin Brennan
Robin Ward