Rework Webform Submission rendering to use EntityViewController.

@see https://drupal.stackexchange.com/questions/246561/how-do-i-add-elements-...

Problem

Webform submissions are being rendered using a custom controller and templates

Solutions

Rework Webform Submission rendering to use EntityViewController.

Notes

• All submissions should be rendered via \Drupal\Core\Entity\EntityViewBuilder::view
• The outputted array should be available to hook_webform_submsision_view_alter().

Tasks

• Setup WebformSubmissionViewController
• Copy \Drupal\node\Controller\NodeViewController
• Proxy old rendering behavior
• Move templates into view controller
• Delete the below templates and preprocessors

Routes to be updated

• entity.webform_submission.canonical
• entity.webform_submission.table
• entity.webform_submission.text
• entity.webform_submission.yaml

Templates to be deleted

• webform-submission.html.twig
• webform-submission-yaml.html.twig
• webform-submission-text.html.twig
• webform-submission-table.html.twig
• webform-submission-html.html.twig

API Changes

Major reworking and simplification of webform submission rendering.