Stuck after file upload validation

When uploading several files and an upload validation for one file fails, the user can only remove the files that pass validation, but not continue the process as the Upload button is hidden via .js-hide by the managed file field.

Proposed resolution

Just remove all uploaded files. This need "just" un-commenting some lines in FileUploadForm::validateUploadElement. (This is also what media_library does.)

Or make a new button appear, if the formstate has errors, but also files ready to upload, named Process all (selected and un-selected). Or even make the user select the files to process, by default all are de-selected because of the *Remove selected* button. Maybe even addressed in core(regular use of the managed file filed on a node-edit page still have the Save or Create button ..), but I guess the AJAX behaviors should be covered by the implementation ..