Only sync selected categories as product type

[mikkamp]

Changes proposed in this Pull Request:

This PR changes the behaviour to only sync the selected categories as product type. Previously it would sync parent categories, both included as the parent of a child category as well as the parent individually even if the parent wasn't selected directly.

This change switches from using wc_get_product_cat_ids to using wc_get_product_term_ids as the first function will include a list of ancestors (regardless of whether they are selected or not). The latter function will return a list of all the selected categories. Which means we can influence which parent categories get synced individually by selecting them or not.

I altered the unit test to match the expected behaviour as well as testing some more edge cases to ensure they are synced correctly:

• test for unselected parent not included
• test 2 levels of ancestors
• test parent and child are included individually when both are selected
• test unrelated category is not included

Closes #2230

Detailed test instructions:

1. Setup a site with the extension and onboarded to Merchant Center
2. Create some categories with hierarchy
3. Create a test product where only the child category is selected
   
4. Save the product and wait for it to sync, and then confirm the final attributes in MC, the parent category should not be included as an individual line
   
5. Create a test product where both the parent and child categories are selected
   
6. Save the product and wait for it to sync, and then confirm the final attributes in MC, the parent category should be included as an individual line and also as part of the child line
   

Changelog entry

• Fix - Only sync selected categories as product type.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (876e3fe) 60.1% compared to head (8f886e3) 60.1%.
Report is 1 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##             develop   #2233   +/-   ##
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  Coverage       60.1%   60.1%           
  Complexity      4141    4141           
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  Files            454     454           
  Lines          17586   17586           
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  Hits           10572   10572           
  Misses          7014    7014           

Flag	Coverage Δ
php-unit-tests	60.1% <100.0%> (ø)

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Files	Coverage Δ
src/Product/WCProductAdapter.php	97.8% <100.0%> (ø)

[martynmjones]

Hey @mikkamp, thanks for the fix.

Tested syncing products with different category selections to confirm it will sync with:

• Only the parent category
• Parent and child categories
• Child categories only

LGTM ✅