Refactor the Configurable Product form

[naydav]

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[HLD] Inconsistent saving of Stock Data

Description

For this refactoring, you will need to:

• update the Configurations section in configurable product form (creating and updating)
• remove logic from \Magento\ConfigurableProduct\Model\Product\VariationHandler

if (!isset($postData['stock_data']['is_in_stock'])) {
    $stockStatus = $parentProduct->getQuantityAndStockStatus();
    $postData['stock_data']['is_in_stock'] = $stockStatus['is_in_stock'];
}