addExpressionFieldToSelect has to be called after all addFieldToSelect bug fix

[magently]

Description

lib/internal/Magento/Framework/Model/ResourceModel/Db/Collection/AbstractCollection.php
addExpressionFieldToSelect() method added it's result to getSelect()->columns. When you called addFieldToSelect() method after addExpressionFieldToSelect() expressions where removed from columns. Your select was overwriten by addFieldToSelect(). To avoid that i changed the addExpressionFieldToSelect() method to insert it's result into $this->_fieldsToSelect array as \Zend_Db_Expr. This way it does not get overwritten and you get results from both methods in your collection no matter the order you call them in.

Fixed Issues (if relevant)

1. addExpressionFieldToSelect has to be called after all addFieldToSelect #17635

Manual testing scenarios

• create a collection
• before the change the following code will only show finish_date in collection:
  $bookingCollection = $this->_bookingCollectionFactory->create();
  $bookingCollection->addExpressionFieldToSelect('stime_part', 'time(start_time)', []);
  $bookingCollection->addFieldToSelect('finish_time', 'finish_date');
  -after proposed change you will see both stime_part and finish_date

[magento-engcom-team]

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[okorshenko]

Hi @magently
Thank you for your contribution and welcome to Magento Community!
It would be great if you can cover your improvements with the integration test.
Thank you

[sidolov]

Hi @magently , I'm closing this PR as duplicate for #17915