Stepper: Fix how isNewAccount is calculated

[escapemanuele]

Proposed Changes

Change how isNewAccountCreated is calculated in Stepper during account creation. This makes it similar to how Start calculates it.
It will later be used, upon signup flow completion, to trigger calypso_new_user_site_creation.

Why are these changes being made?

There is a big discrepancy in the calypso_new_user_site_creation event, with Stepper logging a really low number.

Testing Instructions

• Live link
• Go through the onboarding flow in Stepper and in Start and check that both have the same events triggered.
• Check for calypso_new_user_site_creation and calypso_signup_complete

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-122203

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-122203&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-122203&env=a8c-for-agencies

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[renancarvalho]

Comparing side by side calypso_signup_complete I can see that is_new_site property is being logged correctly or at least equally.

start

• blog_id: 238150157 Blog RC
• blog_lang: en
• client: browser
• elapsed_time_since_start: 35099
• environment: production
• environment_id: wpcalypso
• flow: onboarding
• framework: start
• has_cart_items: true
• is_blank_canvas: false
• is_new_site: true
• is_new_user: false
• plan_product_slug: personal-bundle
• signup_domain_origin: free
• site_count: 186
• site_id_label: wpcom
• site_plan_id: 1
• user_lang: en
• vph: 1006
• vpw: 2047

setup

• blog_id: 238150234 Blog RC
• client: browser
• elapsed_time_since_start: 182776
• environment: production
• environment_id: wpcalypso
• flow: onboarding
• framework: stepper
• has_cart_items: true
• intent: onboarding
• is_blank_canvas: false
• is_new_site: true
• is_new_user: false
• plan_product_slug: personal-bundle
• signup_domain_origin: free
• site_count: 185
• site_id_label: wpcom
• starting_point: onboarding
• theme:
• user_lang: en
• vph: 1006

I was unable to see calypso_new_user_site_creation event in both start and setup.