[Woo POS] [Variable Products] Add WC 9.7+ downloadable parameter to variations request

[jaclync]

Part of #14871

Description

I decided to only PR the WC 9.7+ parameter addition without the local filter for easier testing. There will be a future PR for the local filter to filter out downloadable variations for < 9.7.

This pull request introduces a new downloadable parameter to ProductVariationsRemote and updates related tests in ProductVariationsRemoteTests. The most important changes include adding the downloadable parameter to the request methods and ensuring that the correct parameters are set in the tests.

Updates to ProductVariationsRemote class:

• Added the downloadable parameter to the productVariationsRequest method and updated the method signature to include this new parameter.
• Included the downloadable parameter in the request parameters dictionary.
• Added a new constant for the downloadable parameter key in the ParameterKey extension.

Updates to tests:

• Added a new test test_loadVariationsForPointOfSale_sets_correct_parameters to verify that the downloadable parameter is correctly set when loading variations for a point of sale.
• Added a new test test_loadAllProductVariations_sets_correct_parameters to verify that the downloadable parameter is not set when loading all product variations.

Steps to reproduce

Prerequisite: the store has a variable product with a downloadable variation. This can only be set in wp-admin, not in the app. The WC plugin in the store can be managed manually.

WC version < 9.7

🗒️ As 9.6 is not publicly released yet, you can enable variable products by removing this line.

• Go to Menu > Point of Sale
• Tap on the variable product in the prerequisite --> after loading, the downloadable variation should be visible (since the local filter hasn't been implemented)

WC version 9.7+

• In wp-admin, upload the zip from the nightly build woocommerce-trunk-nightly.zip
• Go to Menu > Point of Sale
• Tap on the variable product in the prerequisite --> after loading, the downloadable variation should not be visible

Testing information

I tested it with WC version 9.7.0-dev.

Screenshots

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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.

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.487

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS
	Build Number	pr14893-3969b45
	Version	21.4
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	3969b45
	App Center Build	WooCommerce - Prototype Builds #12557

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[staskus]

Thanks, works well.

Downloadable variations are no longer visible on 9.7.