DEV: Change create-invite-uploader to use uppy (PR #15088)

Part of overall strategy to remove jQuery file uploader from the codebase. Also added some helper functionality to the uppy mixin to allow for non-autostart uploads (all previous upload changes have been for auto start components.)


Minor nit: since you’re using _uppyInstance without ?. above, it means it either will fail earlier or this ?. isn’t needed

much code removed makes me happy, feel free to merge once you address @CvX’s comment.

Yep will look at getting this merged today @SamSaffron , was just sorting the upload handler + making uppy default in composer stuff first.