ECE: enforce separate location settings

[annemirasol]

Fixes STRIPE-286
Fixes #3935

Changes proposed in this Pull Request:

• Fixes the issue where the Amazon Pay button shows up inside the Customize page for Apple Pay/Google Pay
• Fixes the issue where location settings for Amazon Pay and Apple Pay/Google Pay can affect each other.

Testing instructions

1. Enable the Amazon Pay feature flag: wp option update _wcstripe_feature_amazon_pay yes
2. Enable Amazon Pay express checkout.
3. Go to Customize, and enable it only for Checkout.
4. Enable Apple Pay/Google Pay.
5. Go to Customize, and disable it for Checkout.
6. Confirm Amazon Pay shows up on checkout, while Google Pay and Apple does not, but they show up on the other pages

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• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

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Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)

[wjrosa]

Hey @annemirasol! I will be tackling this PR. It still lacks some frontend changes. I will work on those