Fix incorrect grouped product qty returned in GraphQL due to hydration overwriting link attributes

[mimou78]

Description

This pull request fixes an issue where GraphQL returns incorrect or inconsistent qty values for grouped product links.
During GraphQL hydration, the Product::getQty() value is overwritten because it represents a mutable runtime value rather than the original link attribute qty stored in the database.

This causes:

• GraphQL to return wrong qty values (often 1)
• REST API to return correct qty values
• Multiple hydration passes to overwrite values in memory

This PR ensures that GraphQL consistently uses the original link quantity via getInitialQty() (or an equivalent stable fallback), preventing overwriting and ensuring parity between REST and GraphQL.

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Related Pull Requests

None.

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Fixed Issues

• Fixes [GraphQl] Order of graphql request changes value for default qtys on grouped product. #40286

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[mimou78]

@magento run Unit Tests

[mimou78]

@magento run all tests

[mimou78]

@magento run all tests