Billing: Update ChangePaymentMethod to use PaymentMethodSelector

[sirbrillig]

Changes proposed in this Pull Request

This abstracts the payment method list and assignment code from ChangePaymentMethod into its own component called PaymentMethodSelector. The primary purpose of this is to enable reusing that component in other payment method forms like AddNewPaymentMethod.

Part of #48966

Depends on #49057

Testing instructions

• Visit the subscription page for a purchase that already has a payment method assigned.
• Click on the "Change payment method" button.
• Verify that the list of payment methods appears.
• Select the "new" credit card payment method, fill it in, and submit the form.
• Verify that you are redirected to the subscription page with a success message.
• Verify that the new payment method is created and assigned to the subscription.
• Repeat the above steps but select an existing card and verify that everything works as before.

[matticbot]

Test live: https://calypso.live/?branch=update/change-payment-method-to-use-payment-method-selector

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~30 bytes removed 📉 [gzipped])

name                   parsed_size           gzip_size
entry-main                   -38 B  (-0.0%)      -30 B  (-0.0%)
entry-login                  -38 B  (-0.0%)      -30 B  (-0.0%)
entry-gutenboarding          -38 B  (-0.0%)      -30 B  (-0.0%)
entry-domains-landing        -38 B  (-0.0%)      -30 B  (-0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Sections (~49 bytes removed 📉 [gzipped])

name            parsed_size           gzip_size
site-purchases       +946 B  (+0.1%)     +149 B  (+0.0%)
purchases            +946 B  (+0.1%)     +149 B  (+0.0%)
woocommerce          -413 B  (-0.0%)     -194 B  (-0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[nbloomf]

Works as described in both the site level and account level contexts.

[sirbrillig]

Rebased after some changes to notifications landed. Testing it still works as far as I can tell.

[a8ci18n]

This Pull Request is now available for translation here: https://translate.wordpress.com/deliverables/5487305

Thank you @sirbrillig for including a screenshot in the description! This is really helpful for our translators.

[a8ci18n]

Translation for this Pull Request has now been finished.