Update ECE deafult button and button position in shortcode cart page

[Mayisha]

Changes proposed in this Pull Request:

Made two tiny design updates in this PR.

1. Made the icon-only option the default one for express checkout buttons (like WooPayments). When you install the Stripe plugin on a new site and enable Google/Apple Pay, the default button will be icon-only.
2. Fixed the ECE button position on the shortcode cart page.

Testing instructions

Case 1:

• Build this branch and upload the zip to a fresh site (JN site). Enable Google/Apple pay and confirm that the default selected button type is icon only.

Case 2:

• Install the PayPal plugin in your site and complete setup. (Instead of PayPal you may also use any other payment gateway that would show the payment button on the shortcode cart page).
• Add a product to your cart and go to the shortcode cart page.
• In develop branch, notice that the ECE button is placed above.

• In this branch, confirm that the ECE button is placed with other payment buttons.

[annemirasol]

LGTM 🚢 🚢

1. Making "Icon only" default for new installs: works as expected ✨
2. Removing separator for shortcode cart: works as expected ✨

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Listing some additional findings here -- I'm not really sure that these are issues. If you think they are, we can create separate trackers for them.

1. I noticed that for ECE, "Icon only" vs "Buy" does not really change the Google Pay icon when the customer is logged in. "Donate" and "Book" change the button as expected. It works fine though when the customer is logged out.

Icon only (logged in)	Buy (logged in)	Donate	Book

2. When all three are present, it looks like this for shortcode cart:

For comparison, it looks like this in block cart, i.e. each button in its own row:

[Mayisha]

Thanks @annemirasol

When all three are present, it looks like this for shortcode cart:

I will look into this 👀