Split upe w' deferred intent - don't display APMs on classic checkout while auth and capture is enabled

[james-allan]

Fixes #2923

Changes proposed in this Pull Request:

When you enable authorize and capture in the Stripe plugin settings, a modal pops up to explain that only card payments will be available while using auth and capture.

This works as expected on the block checkout, however it doesn't on the classic checkout. All APMS were being shown even though auth and capture were enabled.

This PR fixes that.

Testing instructions

1. Under WooCommerce > Settings > General, set the store currency to EUR
2. Under the Stripe Payment methods tab, enable all available APMs.
3. Under the Stripe Settings tab, enable the Updated Checkout Experience and the 'authorization on checkout, and capture later' setting.
4. As a shopper, add a product to your cart and go to the classic checkout.
   • On the add/deferred-intent branch notice all APMs are displayed.
   • On the this branch only cards are shown.
5. Turn off authorize and capture and all payment methods should be now shown again.

---

• Covered with tests (or have a good reason not to test in description ☝️)
• Added changelog entry in both changelog.txt and readme.txt (or does not apply)
• Tested on mobile (or does not apply)

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)

[mattallan]

Thanks @james-allan for the PR. The code changes look good to me and tests well. I just made a small suggestion on the inline comment to clarify how the UPE gateway function is called.

• With Authorize and Capture enabled 👍

develop	fix/2923

• With capture immediately 👍