Soundcloud embed Formatter should only be available for Media entity fields

Problem/Motivation

When changing the order of link / string/ string_long types of fields on the manage display (maybe only in combination with Field Group order changes that messes things up a bit), Field Formatter type can get changed to "Soundcloud embed", resulting in the error shown below.

Proposed resolution

It should actually only be possible to choose that Field Formatter when the field type is a media field.

Remaining tasks

Create a patch and review.

Error message

Error: Call to undefined method Drupal\node\Entity\Node::getSource() in Drupal\media_entity_soundcloud\Plugin\Field\FieldFormatter\SoundcloudEmbedFormatter->viewElements() (line 111 of /var/www/html/web/modules/contrib/media_entity_soundcloud/src/Plugin/Field/FieldFormatter/SoundcloudEmbedFormatter.php)

#0 /var/www/html/web/core/lib/Drupal/Core/Field/FormatterBase.php(80): Drupal\media_entity_soundcloud\Plugin\Field\FieldFormatter\SoundcloudEmbedFormatter->viewElements(Object(Drupal\Core\Field\FieldItemList), 'en')
#1 /var/www/html/web/core/lib/Drupal/Core/Entity/Entity/EntityViewDisplay.php(263): Drupal\Core\Field\FormatterBase->view(Object(Drupal\Core\Field\FieldItemList), 'en')
#2 /var/www/html/web/core/lib/Drupal/Core/Entity/EntityViewBuilder.php(321): Drupal\Core\Entity\Entity\EntityViewDisplay->buildMultiple(Array)
#3 /var/www/html/web/core/modules/node/src/NodeViewBuilder.php(22): Drupal\Core\Entity\EntityViewBuilder->buildComponents(Array, Array, Array, 'popup')
#4 /var/www/html/web/core/lib/Drupal/Core/Entity/EntityViewBuilder.php(263): Drupal\node\NodeViewBuilder->buildComponents(Array, Array, Array, 'popup')
#5 /var/www/html/web/core/lib/Drupal/Core/Entity/EntityViewBuilder.php(220): Drupal\Core\Entity\EntityViewBuilder->buildMultiple(Array)
#6 [internal function]: Drupal\Core\Entity\EntityViewBuilder->build(Array)
#7 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(378): call_user_func(Array, Array)
#8 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, true)
#9 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(139): Drupal\Core\Render\Renderer->render(Array, true)
#10 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(582): Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}()
#11 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(140): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure))
#12 /var/www/html/web/modules/contrib/leaflet/leaflet_views/src/Controller/LeafletAjaxPopupController.php(85): Drupal\Core\Render\Renderer->renderRoot(Array)
#13 [internal function]: Drupal\leaflet_views\Controller\LeafletAjaxPopupController->popupBuild(Object(Drupal\node\Entity\Node), 'popup', 'en')
#14 /var/www/html/web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array)
#15 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(582): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#16 /var/www/html/web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure))
#17 /var/www/html/web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array)
#18 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(151): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#19 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#20 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#21 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#22 /var/www/html/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#23 /var/www/html/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#24 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#25 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#26 /var/www/html/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#27 /var/www/html/web/core/lib/Drupal/Core/DrupalKernel.php(693): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#28 /var/www/html/web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#29 {main}