Pass the media library state object to createAccess()

Transferred the code from the merge request in #2993187: Add a media library widget setting to only choose existing media.

Tagging this as a contrib project blocker, since it's needed in order to implement #3224564: Add a media library field widget setting to hide the "add media" form.

Good call, @effulgentsia. I changed it so that the hook actually tries to use the state object to make an access decision.

I take it back. If you look at the code of MediaLibraryUiBuilder, you'll see that it $build['content'] always has a 'form' element (see the buildLibraryContent() method). But it is always going to be absolutely empty if access is denied, per this code at the top of buildMediaTypeAddForm():

    $selected_type_id = $state->getSelectedTypeId();

    $access_handler = $this->entityTypeManager->getAccessControlHandler('media');
    $context = [
      'media_library_state' => $state,
    ];
    if (!$access_handler->createAccess($selected_type_id, NULL, $context)) {
      return [];
    }

So I think that, to prevent further refactoring and scope creep, assertEmpty() and assertNotEmpty() are the correct assertions for us to use.

Replied to all threads; for various reasons, I'm not sure any changes are needed here. So, tentatively restoring RTBC.

Created https://www.drupal.org/node/3225885 to document the change.