Onboarding consistency: Use StepContainerV2 in 'Use domain I own' step

[zaguiini]

Closes #101196.

Proposed Changes

• Adds a "10" column version of the CenteredColumnLayout. It's based on the width of the 5+5 cols two column layout
• Removed the showHeader prop from UseMyDomain component. It was unused
• Added new hideHeader prop to UseMyDomain. This is so we can render the header using <Step.Header> instead. I thought it was better not to reuse the existing showHeader prop because I wanted it to be clear the default is false.
• Wrap the "Use a domain I own" screens in the CenteredColumnLayout wireframe
• Adjust styles so the step paddings follow the mockups.

Fix some design inconsistencies:

• Domain input card has background but no borders, as well as some bottom margin that we can remove

Testing

There should be no changes unless the onboarding/step-container-v2 feature flag is enabled.

The UseMyDomain component is used in multiple places in the UI. We need to find them and ensure nothing has broken.

The second sub-step in the "Use a domain I own" screen has two variants, where sometimes there's two buttons and sometimes there's only one.

• I used google.com to test the case where the domain can not be transferred.
• I used neopets.com to test the case where it could be transferred.

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-138115

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-138115&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-138115&env=a8c-for-agencies

[matticbot]

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

App Entrypoints (~6 bytes added 📈 [gzipped])

name                   parsed_size           gzip_size
entry-stepper               +298 B  (+0.0%)       +6 B  (+0.0%)
entry-subscriptions          -13 B  (-0.0%)      -54 B  (-0.0%)
entry-main                   -13 B  (-0.0%)      -54 B  (-0.0%)
entry-login                  -13 B  (-0.0%)      -54 B  (-0.0%)
entry-domains-landing        -13 B  (-0.0%)      -54 B  (-0.0%)
entry-browsehappy            -13 B  (-0.0%)      -54 B  (-0.1%)

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

Sections (~3615 bytes removed 📉 [gzipped])

name                        parsed_size           gzip_size
async-step-use-my-domain       +24639 B  (+4.3%)    +9687 B  (+5.8%)
stepper-user-step                 -54 B  (-0.0%)     -130 B  (-0.1%)
signup                            -52 B  (-0.0%)      -19 B  (-0.0%)
async-step-unified-plans          -52 B  (-0.0%)      -17 B  (-0.0%)
async-step-unified-domains        -43 B  (-0.0%)      -14 B  (-0.0%)
domains                           +23 B  (+0.0%)      +10 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 (~182 bytes removed 📉 [gzipped])

name                                          parsed_size           gzip_size
async-load-signup-steps-new-or-existing-site        -13 B  (-0.0%)     -182 B  (-0.7%)

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.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• blaze-dashboard
• command-palette-wp-admin
• help-center
• notifications
• odyssey-stats
• whats-new

To test WordPress.com changes, run install-plugin.sh $pluginSlug onboarding/use-my-domain-step-uses-step-container-v2 on your sandbox.

[p-jackson]

Domain input card has background but no borders, as well as some bottom margin that we can remove

@zaguiini I left this as it was since I believe we're not trying to fix up all the inconsistencies within the steps themselves?

[p-jackson]

I asked a question about this sub title here p1742799582663609-slack-C08HKNPL2BG

But it's not a blocker.

[a8ci18n]

This Pull Request is now available for translation here: https://translate.wordpress.com/deliverables/17314216

Some locales (Hebrew, Japanese) have been temporarily machine-translated due to translator availability. All other translations are usually ready within a few days. Untranslated and machine-translated strings will be sent for translation next Monday and are expected to be completed by the following Friday.

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

[a8ci18n]

Translation for this Pull Request has now been finished.