New hook_entity_field_values_init() and hook_entity_translation_create() added

Two new entity hooks with their respective entity-type-specific flavors were added:

• hook_entity_translation_create()
• hook_entity_field_values_init()

Before this change when creating a new entity translation via the ::addTranslation() method the hook_entity_create() was invoked to allow to massage initial field values also for entity translations without duplicating code.

This logic should be now implemented via hook_entity_field_values_init(), while hook_entity_create() and hook_entity_translation_create() should be used when needing to act on their specific cases.

Additionally a new method TranslatableInterface::isNewTranslation() method was added to allow to tell whether an entity translation object has just been instantiated or was already persisted previously.