Replace deprecated usage of entity_create('field_storage_config') with a direct call to FieldStorageConfig::create()

Follow-up to #2490966: [Meta] Replace deprecated usage of entity_create with a direct call to the entity type class

Problem/Motivation

According to #2346261: Deprecate entity_create() in favor of a <EntityType>::create($values) or \Drupal::entityManager()->getStorage($entity_type)->create($values), entity_create() function is going to be deprecated so we shouldn't use it anymore. When the entity type is known we should directly call <EntityType>::create(). What to do when the entity type is not known or is variable is upon discussions.

Beta phase evaluation

Proposed resolution

Replace the deprecated call to entity_create() by a proper call to <EntityType>::create().

Before:

entity_create('field_config', $field_values)->save();

After:

use Drupal\field\Entity\FieldConfig;
FieldConfig::create($field_values)->save();

Remaining tasks

User interface changes

None.

API changes

None.