Use local variable over object in \Drupal\Core\Entity\Sql\SqlContentEntityStorage::loadFromDedicatedTables() for column names

Problem/Motivation

Noticed when reviewing #3593963: Field loading can hit the MySQL 61 table join limit if there are ~60 fields - we do

            // For each column declared by the field, populate the item from
            // the prefixed database column.
            foreach ($field_definition_columns[$field_name] as $column => $attributes) {
              $column_name = $table_mapping->getFieldColumnName($storage_definition, $column);
              // Unserialize the value if specified in the column schema.
              $item[$column] = (!empty($attributes['serialize'])) ? $this->handleNullableFieldUnserialize($row[$column_name]) : $row[$column_name];
            }

for both single cardinality and multiple cardinality fields but we have $field_columns with all the columns name in it already so we should use that instead of $table_mapping.

Proposed resolution

Use $field_columns

Remaining tasks

User interface changes

None

Introduced terminology

N/a

API changes

None

Data model changes

None

Release notes snippet

N/a