[Product Bundles] Add support for parent/child relationships between AggregateOrderItems

[rachelmcr]

Part of #8962

Description

This is part of UI support for displaying the product bundle hierarchy (parent/child relationship between the product bundle and its bundled products) in order details. We use AggregateOrderItem to combine order items and refunded items in order details. This PR adds the parent property to AggregateOrderItem so we can show the parent/child relationship in the UI.

We will use these changes to adjust the product list UI in order details in an upcoming PR.

Changes

• Updates AggregateOrderItem to include parent.
• Updates AggregateDataHelper to set the parent property when combining refunded products and order items. For refunded products, we look for the matching order item and get the parent from there.

Testing instructions

Confirm unit tests pass. We're not yet using this new property anywhere in the app.

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

You can test the changes from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr9777-b9a0a92 on your iPhone

If you need access to App Center, please ask a maintainer to add you.

[ThomazFB]

Looks good!