Variations: Update product variation count after generating variations

[Ecarrion]

Closes: #8551

Why

This PR takes care of updating the variation count of the main product after generating variations. This is needed to properly reflect changes on the main product screen and on the product list.

Demo

demo-updated-products.mov

Testing Steps

• Start the generate all variation process
• After generating the variations go back to the main product screen
• See that the variation count matches the previous variation count + the new generated variations count.

---

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-woocommerce]

	Warnings
⚠️	This PR is assigned to a milestone which is closing in less than 2 days Please, make sure to get it merged by then or assign it to a later expiring milestone

Generated by 🚫 dangerJS

[wpmobilebot]

You can test the changes from this Pull Request by:

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• Then installing the build number pr8612-f0bfd44 on your iPhone

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[rachelmcr]

LGTM! 🚀