Add dedicated integration with Product Bundles

[tomalec]

Changes proposed in this Pull Request:

Add dedicated integration with Product Bundles,
Use ->get_bundle_price( 'min' ); instead of ->get_price() for bundles.

Fixes #219 the simple way.

Checks:

• Does your code follow the WordPress coding standards?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Screenshots:

Detailed test instructions:

1. Install and activate the Product Bundles (PB) extension
2. Add a new bundle product
   
3. Add bundled products that are priced individually
   
4. Publish the product bundle
5. Open the site through https://tagassistant.google.com/
6. Go to the product bundle page
7. Check that view_item event is tracked with the correct bundle price
8. Add the bundle to cart
9. Check that add_to_cart event is tracked with the correct bundle price
10. Uninstall the PB extension and smoke test for regression.

Additional details:

1. I didn't add E2E tests, as PB is a paid extension, and public contributors to this repo would not be able to use it to run E2Es locally. We can try mocking PB interface, but then it's not really E2E. I'm open to better ideas :)

Changelog entry

Add - WooCommerce Product Bundles integration.

[martynmjones]

Hey @tomalec, thanks for working on the fix for bundle pricing!

Events tracked via the classic integration all look to be using the correct values for bundle prices.

There is still an issue with the Block remove_from_cart event. When we're building the product object in JS we're making use of product.prices.price and when a product is removed from cart on a block powered page that value will be the base price:

We could instead rely on totals.line_total for the price if it is available which should give us consistent pricing across different integrations.

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I didn't add E2E tests, as PB is a paid extension, and public contributors to this repo would not be able to use it to run E2Es locally. We can try mocking PB interface, but then it's not really E2E. I'm open to better ideas :)

I don't have much else to suggest here I'm afraid. We could add a unit test in PHP for the bundled price in get_formatted_product which would be a lot easier to mock although that wouldn't cover Blocks.

[tomalec]

Thanks, @martynmjones, for catching that!
I applied your suggestions. Speaking of tests, as there are none for get_formatted_product so far, WDYT of adding them as a follow-up in the next porter or cooldown cycle?

[martynmjones]

Thanks for the changes @tomalec!

Pricing is consistent across different events and integrations now so LGTM ✅

WDYT of adding them as a follow-up in the next porter or cooldown cycle?

Agreed! A follow-up for adding tests sounds good.

[tomalec]

Thanks :) Created the follow-up issue to track tests #442