Improve hook_entity_presave documentation

This commit updates the documentation for the Drupal API page to provide more clarity on accessing the original entity object in a multi-language context. It also suggests alternative methods for retrieving the original translation if $entity->original does not refer to the expected translation. This should help improve understanding for developers working with Drupal in a multi-language context.

Change definitely seems better then before.

But this phrase

* In such cases, you can use other available methods
* to retrieve the original translation.

Feel if we are going to mention that we should mention what those are or least where someone would go to look.

Is this specific to hook_entity_presave or should we update it for hook_entity_update as well? Also note hook_ENTITY_TYPE_presave and hook_ENTITY_TYPE_update also mention $entity->original.

I'm also wondering if it's better to address this in 📌 Add a method to access the original property Needs work where the property is defined rather than in the hook documentation.