Unified Design Picker: Theme Preview recognizes individual premium theme purchases

[mreishus]

Proposed Changes

• When using the Unified Design Picker and previewing an individual premium theme, check to see if that theme has been purchased when deciding to display the "Unlock " button

Current behavior

With this PR

Testing Instructions

• Have a free site with an individual premium theme purchased
• Go to /setup/designSetup?siteSlug=<SITE_SLUG>&flags=signup/seller-upgrade-modal (note the flag)
• Find a Premium theme you have purchased, and click on it to preview
• The top right button should say "Start with ThemeName" and not "Unlock"
• Click back, and this time click on a Premium theme you have not purchased
• The top right button should continue to say "Unlock"

Related to #65857 #66187

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-39057

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-39057&env=jetpack

[matticbot]

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

App Entrypoints (~4990 bytes added 📈 [gzipped])

name           parsed_size           gzip_size
entry-stepper     +19565 B  (+0.5%)    +4990 B  (+0.5%)

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

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.

[markbiek]

LGTM!