Expose attribute mapping rule values using WCProductAdapter

[jorgemd24]

Changes proposed in this Pull Request:

Part of #2146

This is an alternative for #2351.

Rather than moving the attribute logic from WCProductAdapter into the AttributeManager, we're now crating an instance of WCProductAdapter to retrieve all aggregated attribute values from particular products. Similar to the other PR, we'll use these attribute values to expose them in the WC REST Product endpoints. For additional context, refer to #2351.

Screenshots:

Detailed test instructions:

1. Go to GLA -> Attribute -> Create some rules.
2. Make the following request GET wc/v3/products?gla_syncable=1 or GET wc/v3/products/YOUR_PRODUCT_ID?gla_syncable=1
3. See that the response contains a new property named: gla_attributes with the correct values.

4. Update the products by adding a GLA Attribute. This attribute should take precedence over any mapping rule applied to the same attribute.

5. Remove the query parameter gla_syncable=1 and the response should not contain gla_attributes.
6. Repeat the steps for a variation product using the following endpoint: wc/v3/products/PARENT_ID/variations/VARIATION_ID?gla_syncable=1

Additional details:

• PHP unit tests are failing because of this issue: Get Plugin Releases - Prevent un-stable version to be fetched. grow#101 but you can run the tests locally.

Changelog entry

[puntope]

Thanks for adapting the PR to reduce code duplication.

It is working as expected for me. ✅