loadFromDedicatedTables(): getColumnNames() returns nothing for bundle fields, so BundleFieldDefinition fields load with NULL values and emit "Undefined array key" warning

Problem/Motivation

Steps to reproduce

1. Drupal 11.4.x on PHP 8.x.
2. Install Commerce + Commerce Shipping 3.x; enable shipping on an order type.
3. Create an order and add a shipment to it.
4. Load the order via the entity API (or view the cart block / order admin).
5. Observe the two Undefined array key warnings, and that $order->get('shipments')->first()->target_id is NULL.

Minimal, non-Commerce: define a BundleFieldDefinition entity-reference field with cardinality > 1 (dedicated-table storage) on any content entity, save a value, then load the entity.

Proposed resolution

Build $field_columns from the field's own storage definition (already in scope in the loop), as the code did before #3594426. This is identical to getColumnNames() for base/config fields, and correctly populated for bundle fields:

$field_columns[$field_name] = [];
foreach (array_keys($storage_definition->getColumns()) as $property_name) {
  $field_columns[$field_name][$property_name] = $this->tableMapping->getFieldColumnName($storage_definition, $property_name);
}

Patch attached; verified on a production-bound Commerce site (shipments load with real target_ids, warnings gone).

Remaining tasks

• Confirm the approach (vs. teaching getColumnNames() to fall back to the passed storage definition).
• Add test coverage: load an entity with a dedicated-table BundleFieldDefinition field (single- and multi-cardinality) and assert values load without warnings.
• Reviews / MR against 11.4.x and 11.x.

User interface changes

None.

Introduced terminology

None.

API changes

None. Restores the pre-11.4.0 behavior of loadFromDedicatedTables(); no public method signatures change.

Data model changes

None.

Release notes snippet

Fixed a regression from 11.4.0 where loading a content entity that has a bundle field (BundleFieldDefinition) stored in a dedicated table populated that field with empty/NULL values and triggered "Undefined array key" warnings. Notably, this restores loading of Commerce Shipping's order shipments field.