Function bwc_paypal_checkout_flow

Return true if the PayPal checkout flow is 'checkout.' If WooCommerce Subscriptions is active, then check if the cart contains subscriptions. If there are subscriptions in the cart, then 'vault' must be active to ensure PayPal payment methods are saved. If the page is the add payment page, then false is returned as 'vault' flow is needed for adding PayPal payment methods.