Drupal 9 Call to undefined function Drupal\media_library_importer\Form\drupal_set_message()

Problem/Motivation

On sites using Drupal 9, a website error occurs when attempting to import due to a deprecated function being used in src/Form/ImportForm.php

The website encountered an unexpected error. Please try again later.
Error: Call to undefined function Drupal\media_library_importer\Form\drupal_set_message() in Drupal\media_library_importer\Form\ImportForm::batchMediaCreationFinished() (line 184 of modules/contrib/media_library_importer/src/Form/ImportForm.php).
Drupal\media_library_importer\Form\ImportForm::batchMediaCreationFinished(1, Array, Array, Object) (Line: 456)
_batch_finished() (Line: 98)
_batch_page(Object) (Line: 55)
Drupal\system\Controller\BatchController->batchPage(Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 573)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 158)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 80)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 67)
Drupal\simple_oauth\HttpMiddleware\BasicAuthSwap->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 706)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

1. Log into a site using Drupal 9
2. Go to /admin/config/media/media-library-importer/import
3. Select any media
4. Press submit
5. See error

Proposed resolution

Update the referenced drupal_set_message function with Messenger service.