Form validation error messages within the Media Library widget are not read by the screenreader

1. +++ b/core/modules/media_library/src/Form/AddFormBase.php
   @@ -857,4 +858,32 @@ protected function isAdvancedUi() {
   +    $response->addCommand(new ReplaceCommand('[data-drupal-selector="' . $form['#attributes']['data-drupal-selector'] . '"]', $form));
   

   We changed the selector from #media-library-add-form-wrapper (which is outside the form) to the inner form - is that intended?

   Do we end up with several nested wrappers?

2. +++ b/core/modules/media_library/src/Form/AddFormBase.php
   @@ -857,4 +858,32 @@ protected function isAdvancedUi() {
   +      $message = is_array($error) ? reset($error) : (string) $error;
   +      $response->addCommand(new MessageCommand($message, '.media-library-widget-modal [data-drupal-messages-fallback]', ['type' => 'error']));
   

   If it is an array, what happens to the other entries in the array?

3. +++ b/core/modules/media_library/src/Form/AddFormBase.php
   @@ -857,4 +858,32 @@ protected function isAdvancedUi() {
   +    // The drupal messages fallback defaults to having the .hidden class, but
   

   nit Drupal not drupal

4. +++ b/core/modules/media_library/src/Form/AddFormBase.php
   @@ -857,4 +858,32 @@ protected function isAdvancedUi() {
   +    // should be visible for this usage.
   

   Why is this the case? It would be good to elaborate a bit more here

5. +++ b/core/modules/media_library/src/Form/AddFormBase.php
   @@ -857,4 +858,32 @@ protected function isAdvancedUi() {
   +    $response->addCommand(new InvokeCommand('.media-library-widget-modal [data-drupal-messages-fallback]', 'removeClass', ['hidden']));
   

   Drupal.Message.defaultWrapper seems to do this already in messages.js - should we be deferring to that?

6. +++ b/core/modules/media_library/tests/src/FunctionalJavascript/MediaLibraryTestBase.php
   @@ -456,4 +456,22 @@ protected function assertSelectedMediaCount($text) {
   +      return strpos($announce->getText(), $expected_message) !== FALSE;
   

   We can use str_contains here now

This actually may need some more thought.

I tested again with the patch but this time using an image field vs media library and this patch. doesn't fix it. Think we should come up with a solution to make sure duplicate messages just don't appear.

@larowlan any suggestion.

At this time changes are not neede for #50 as a new solution is needed