Don't fatal when applied to entity types without a canonical link tempalte

Problem/Motivation

When you use this formatter for example with paragraphs it causes a fatal:

"
An AJAX HTTP error occurred.
HTTP Result Code: 500
Debugging information follows.
Path: /node/2807/edit?ajax_form=1&_wrapper_format=drupal_ajax
StatusText: Internal Server Error
ResponseText: The website encountered an unexpected error. Please try again later.Drupal\Core\Entity\Exception\UndefinedLinkTemplateException: No link template 'canonical' found for the 'paragraph' entity type in Drupal\Core\Entity\Entity->toUrl() (line 215 of core/lib/Drupal/Core/Entity/Entity.php). Drupal\smart_trim\Plugin\Field\FieldFormatter\SmartTrimFormatter->viewElements(Object, 'en') (Line: 80)
Drupal\Core\Field\FormatterBase->view(Object, 'en') (Line: 259)
Drupal\Core\Entity\Entity\EntityViewDisplay->buildMultiple(Array) (Line: 320)
Drupal\Core\Entity\EntityViewBuilder->buildComponents(Array, Array, Array, 'preview') (Line: 263)
Drupal\Core\Entity\EntityViewBuilder->buildMultiple(Array) (Line: 18)
Drupal\paragraphs\ParagraphViewBuilder->buildMultiple(Array) (Line: 220)
Drupal\Core\Entity\EntityViewBuilder->build(Array)
call_user_func(Array, Array) (Line: 378)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 195)
Drupal\Core\Render\Renderer->render(Array) (Line: 490)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 183)
__TwigTemplate_98cf6ee9c325be56e5f6e2b50b209532e42534eaeb86ca76b1fbc0eee1a03602->doDisplay(Array, Array) (Line: 432)
Twig_Template->displayWithErrorHandling(Array, Array) (Line: 403)
Twig_Template->display(Array) (Line: 411)
Twig_Template->render(Array) (Line: 64)
twig_render_template('core/themes/classy/templates/dataset/table.html.twig', Array) (Line: 384)
Drupal\Core\Theme\ThemeManager->render('table', Array) (Line: 437)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 195)
Drupal\Core\Render\Renderer->render(Array) (Line: 490)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 48)
__TwigTemplate_98360c133351f86c9c3ad73c8c67ad64d30fa101e86683f7e236ff6c3c754c0f->doDisplay(Array, Array) (Line: 432)
Twig_Template->displayWithErrorHandling(Array, Array) (Line: 403)
Twig_Template->display(Array) (Line: 411)
Twig_Template->render(Array) (Line: 64)
twig_render_template('core/themes/classy/templates/form/field-multiple-value-form.html.twig', Array) (Line: 384)
Drupal\Core\Theme\ThemeManager->render('field_multiple_value_form', Array) (Line: 437)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 195)
Drupal\Core\Render\Renderer->render(Array) (Line: 490)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 183)
__TwigTemplate_98cf6ee9c325be56e5f6e2b50b209532e42534eaeb86ca76b1fbc0eee1a03602->doDisplay(Array, Array) (Line: 432)
Twig_Template->displayWithErrorHandling(Array, Array) (Line: 403)
Twig_Template->display(Array) (Line: 411)
Twig_Template->render(Array) (Line: 64)
twig_render_template('core/themes/classy/templates/dataset/table.html.twig', Array) (Line: 384)
Drupal\Core\Theme\ThemeManager->render('table', Array) (Line: 437)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 195)
Drupal\Core\Render\Renderer->render(Array) (Line: 490)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 48)
__TwigTemplate_98360c133351f86c9c3ad73c8c67ad64d30fa101e86683f7e236ff6c3c754c0f->doDisplay(Array, Array) (Line: 432)
Twig_Template->displayWithErrorHandling(Array, Array) (Line: 403)
Twig_Template->display(Array) (Line: 411)
Twig_Template->render(Array) (Line: 64)
twig_render_template('core/themes/classy/templates/form/field-multiple-value-form.html.twig', Array) (Line: 384)
Drupal\Core\Theme\ThemeManager->render('field_multiple_value_form', Array) (Line: 437)
Drupal\Core\Render\Renderer->doRender(Array, 1) (Line: 195)
Drupal\Core\Render\Renderer->render(Array, 1) (Line: 139)
Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}() (Line: 576)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 140)
Drupal\Core\Render\Renderer->renderRoot(Array) (Line: 858)
drupal_render_root(Array) (Line: 83)
Drupal\Core\Render\MainContent\AjaxRenderer->drupalRenderRoot(Array) (Line: 62)
Drupal\Core\Render\MainContent\AjaxRenderer->renderResponse(Array, Object, Object) (Line: 89)
Drupal\Core\Form\FormAjaxResponseBuilder->buildResponse(Object, Array, Object, Array) (Line: 98)
Drupal\Core\Form\EventSubscriber\FormAjaxSubscriber->onException(Object, 'kernel.exception', Object) (Line: 108)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.exception', Object) (Line: 230)
Symfony\Component\HttpKernel\HttpKernel->handleException(Object, Object, 1) (Line: 79)
Symfony\Component\HttpKernel\HttpKernel->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: 99)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 657)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)
"

Proposed resolution

Check first whether there is a canonical link template.

Remaining tasks

User interface changes

API changes

Data model changes