Overlay above collection view to show progress of uploaded files via drag & drop

[bjarnef]

Mentioned in #18148

Perhaps it is just me or would a simple progress bar look more clean/slick .. imagine uploading 20 files :)

I like something like these examples:
https://www.uinkits.com/components/file-upload-ui-element
https://vaadin.com/docs/latest/components/upload

Perhaps just show an overlay with progress and refresh view + tree when finished?

Maybe it need some configuration or options to extend. Some may prefer it not upload directly, but one could see a list of files with preview, size, name etc. and button to start upload.
Some upload components allow to cancel uploads, e.g. a large file, which the content editor may want to remove from uploaded files.