Clicking the toggle on Settings > Payments results in a (possibly unnecessary) redirect

[jorgeatorres]

Describe the bug

Context: The enable/disable toggle that appears on WC > Settings > Payments either automatically enables/disables a gateway or redirects to the gateway settings screen if said gateway "needs setup" (controlled by WC_Payment_Gateway::needs_setup()).

In PayPal Payments this method always returns true, which results in a redirect that could be skipped when all the API details have already been filled out and the merchant just wants to quickly enable/disable the gateway.

To reproduce

1. Complete onboarding or fill out all the relevant API details.
2. Go to WooCommerce > Settings > Payments.
3. Scroll down to "PayPal" and make sure the toggle is in the disabled state.
4. Click the toggle.
5. Confirm that instead of the gateway being enabled, you are redirected to the settings screen.

Screenshots

Screencast showing a redirect takes place when trying to enable the gateway via the toggle, even when the gateway is correctly configured:

Expected behavior

needs_setup() should accurately reflect the gateway situation. If API credentials have been stored, needs_setup() should return false.