XSS validation on upload and not only display

Looks like it could be done with a simple hook_file_insert():

/**
 * Implements hook_file_insert().
 */
function svg_image_file_insert(FileInterface $file) {
  $fileUri = $file->getFileUri();
  if (file_exists($fileUri) && $file->getMimeType() === 'image/svg+xml') {
    // Make sure that the SVG file is safe.
    $rawSvg = file_get_contents($fileUri);
    $sanitizedSvg = (new Sanitizer())->sanitize($rawSvg);
    file_put_contents($fileUri, $sanitizedSvg);
  }
}

Created MR, please review.

Thank you @mably ! That is what I had in mind as well but no time yet to manage it.