Domains: Update RegisterDomainStep to use withShoppingCart and remove CartData

[sirbrillig]

Changes proposed in this Pull Request

This replaces the CartData wrapper around RegisterDomainStep with withShoppingCart. This will help us eventually remove CartData (see #24019).

The only thing I wasn't able to determine is if there was a reason why CartData was only being used in signup if 'launch-site' === this.props.flowName. If the cart should be ignored otherwise, we may need to add some additional logic inside RegisterDomainStep to ignore cart in that case. That code originated in #42162 so I'm pinging @eltongo for advice!

Testing instructions

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[matticbot]

Test live: https://calypso.live/?branch=update/register-domain-step-with-shopping-cart

[matticbot]

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

Sections (~24 bytes added 📈 [gzipped])

name     parsed_size           gzip_size
domains        +55 B  (+0.0%)      +24 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.

Async-loaded Components (~3322 bytes added 📈 [gzipped])

name                             parsed_size           gzip_size
async-load-signup-steps-domains     +11260 B  (+4.2%)    +3322 B  (+5.1%)

React components that are loaded lazily, when a certain part of UI is displayed for the first time.

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.

[eltongo]

LGTM! We can definitely pass the cart data regardless of what the current flow is.