PayPal Subscription initiated without a WooCommerce order (2415)

[pedrosilva-pt]

PR Description

This PR adds a reusable validateCheckoutForm function and uses in on subscription product order creation.

Issue Description

User reported that one of their clients bought a subscription through PayPal subscriptions and a WC order ID was not created. The logs show that for PayPal subscriptions involve using the PayPal API at https://api-m.paypal.com/v2/checkout/orders/*ORDERID*. This action happens three times as seen in the logs.

Steps To Reproduce

• set up subscription with connection to PayPal
• add it to cart & navigate to Checkout page
• leave out any required field, like the terms checkbox or name
• click the PayPal button
• observe no form field validation
• confirm PayPal payment in poup window
• observe WooCommerce error message about missing fields
• fill missing fields
• click PayPal button again to confirm order
• observe the user now has two active PayPal Subscriptions

Expected behaviour

The checkout form fields are validated with the early wc validation when clicking the PayPal button.

Possible cause

The early wc validation does not trigger when the buyer attempts the payment from the Checkout page.

Suggested solution

Implement early WC validation when clicking the button for a PayPal Subscriptions from the Checkout page.