Patterns and synced patterns (reusable blocks)

There's no update hook for the new reusable block field_pattern_category and field_pattern_sync_status fields introduced here. This breaks on a site upgrading from 2.x whenever you attempt to add a new pattern:

The website encountered an unexpected error. Please try again later.<br><br><em class="placeholder">InvalidArgumentException</em>: Field field_pattern_category is unknown. in <em class="placeholder">Drupal\Core\Entity\ContentEntityBase->getTranslatedField()</em> (line <em class="placeholder">587</em> of <em class="placeholder">core/lib/Drupal/Core/Entity/ContentEntityBase.php</em>). <pre class="backtrace">Drupal\Core\Entity\ContentEntityBase->get('field_pattern_category') (Line: 323)
Drupal\gutenberg\Controller\ReusableBlocksController->getBlockAttributes(Object) (Line: 229)
Drupal\gutenberg\Controller\ReusableBlocksController->save(Object, NULL)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 580)
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: 163)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 74)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
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: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 692)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)
</pre>

An upgrade path should be created or documented. Ideally something in an update hook.

I think there might also be an issue with the autosave API path /wp/v2/pages/-1/autosaves no longer being matched by the /\/wp\/v2\/(.*)\/autosaves\?(.*)/g regex when trying to update an existing API path.

I think we should probably add a console.warn() call in the api-fetch before returning the "API handler not found" promise, just so it's easier to easily any missing/breaking REST API implementations in future releases.

Sorry it took a while to get back to this. I like the approach, but it seems like \Drupal::service('config.installer')->installDefaultConfig('module', 'gutenberg') will override any local configuration overrides the sites might have, so we need special handling for it.

I've pushed an update to the branch with the updated logic, feel free to test and review, and let me know if it all makes sense.