#26622 - Check quote item for parentItem instead of parentItemId

[aligent-lturner]

Description (*)

This PR fixes issue #26622 - a "fixed amount for whole cart" discount is calculated incorrectly when a configurable product is first added to the cart. This change is to use getParentItem instead of getParentItemId from the quote item when determining if it should be skipped. This is because parentItem is set when the quote item is created, but parentItemId is only set in its beforeSave function.

Fixed Issues (if relevant)

1. Fixed cart discount calculated incorrectly when product first added to cart. #26622: Fixed cart discount calculated incorrectly when product first added to cart

Manual testing scenarios (*)

1. Create fixed amount discount for whole cart of $1 with no conditions/restrictions
2. Navigate to PDP of configurable product
3. Choose configurable product options and add to cart
4. Confirm that discount is correct ($1) in minicart and/or database.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

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[aligent-lturner]

@ihor-sviziev changes made as requested. Modified existing test case in ValidatorTest class to handle additional quote items with differing combinations of parentItemId and parentItem

[aligent-lturner]

@ihor-sviziev I had to move the functionality into a separate function to reduce the cyclomatic complexity.
Some functional tests are failing, but they appear to be completely unrelated to my changes.

[magento-engcom-team]

Hi @ihor-sviziev, thank you for the review.
ENGCOM-6824 has been created to process this Pull Request

[engcom-Bravo]

✔️ QA Passed

After switching to PR, the discount amount became 1$ instead of 0.50$

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