Try: Add product editor hooks for testing variation extensibility

[joshuatf]

Description

This is a POC for making subscriptions compatible with the new product editor flow. It should be tested in conjuction with https://github.com/woocommerce/woocommerce/pull/44162 demonstrate the use of the product editor hooks.

How to test this PR

Follow the testing instructions in https://github.com/woocommerce/woocommerce/pull/44162.

Product impact

• [ ] Added changelog entry (or does not apply)
• [ ] Will this PR affect WooCommerce Subscriptions? yes/no/tbc, add issue ref
• [ ] Will this PR affect WooCommerce Payments? yes/no/tbc, add issue ref
• [ ] Added deprecated functions, hooks or classes to the spreadsheet