Add the “Live Preview” button on the Theme Detail page

[okmttdhr]

Description

We're to add the “Live Preview” button on the Theme Detail 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 #79219.

Acceptance Criteria

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

Dev Tasks

• Implement feature flag
  • Add a flag for Block Theme Previews #79771
• Implement the button
  • Add the “Live Preview” button on the Theme Detail page #79775
  • Hide the button in cases described in pbxlJb-3Uv-p2#known-issues
• We need to review the copy of the "Open live demo" to avoid confusion with "Live Preview"

Testing

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

Related

• Add a button redirects to Block Theme Previews PoC #78456
• Add the “Live Preview” button on the Themes Showcase page #79219

[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.