Add the “Live Preview” button on the Themes Showcase page

[okmttdhr]

Description

We're to add the “Live Preview” button on the three dots on the Theme Showcase page to bring Block Theme Previews to dotcom. See pbxlJb-3Uv-p2 for more detail.

We have the UI in the comment, but we need to review the copy of "Open live demo" to avoid confusion with "Live Preview".

We can use some of the same code as we do in #79218.

Acceptance Criteria

• We can navigate users to the Live Preview from the Theme Showcase page

Dev Tasks

• We need to review the copy of the "Open live demo" to avoid confusion with the "Live Preview"
• Implement feature flag
  • Add a flag for Block Theme Previews #79771
• Implement the button
  • Create selectors for the Live Preview feature #80017
  • Add the “Live Preview” option on the Themes Showcase page  #80071
  • Hide the button in the following themes;
    • themes with "a static page as a homepage"
    • premium thems
    • WooCommerce themes
    • 3rd party themes

Testing

• Go to the Theme Showcase page
• Make sure the button is shown/hidden
• Make sure the link in the button works

Related

• Add the “Live Preview” button on the Theme Detail page #79218

[okmttdhr]

We need to review the copy of the "Open live demo" to avoid confusion with the "Live Preview"

I'm closing this issue, as we can address this in #80134.