Check use of spl_object_hash()/spl_object_id() in SqlContentEntityStorageSchema

Problem/Motivation

Follow-up from #3616553: replace usage of spl_object_hash() with spl_object_id().

public static function getTemporaryTableMappingPrefix(EntityTypeInterface $entity_type, array $field_storage_definitions, $first_prefix_part = 'tmp_') {
    // Construct a unique prefix based on the contents of the entity type and
    // field storage definitions.

This relies on spl_object_id() which should be unique for a request, but isn't necessarily 1-1 with the contents of the objects. Do we need to actually hash the objects? Or is there something else we can use for the key? If the logic is fine, we should update the comment to explain why spl_object_id() is chosen.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

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