Free Listings + Paid Ads: Use merchant's data to composite the ad previews

[eason9487]

Changes proposed in this Pull Request:

This PR implements an item of the 📌 Client states management and API integration in #1610.

• Fetch the product and site data from API and preload data for compositing the ad previews.
• Extra change: Tweak ScaledText style to prevent the font descender from getting cropped out.
  • Font descender was cropped out:
    
  • After tweak:
    

Screenshots:

Kapture.2022-09-23.at.13.07.14.mp4

Detailed test instructions:

💡 There is an additional backend check that needs to be around, and it will be adjusted in a later PR. Basically, the API integration can be tested for now. To bypass that check, temporarily replace this line with:

return $this->is_google_connected();

Updated: I rebased this PR onto #1693, so it should not need the above local adjustment.

1. Set a logo and site title for your shop: Appearance -> Customize -> Site Identity -> edit Logo and Site Title settings -> click on Publish button.
2. Go to step 4 of onboarding flow.
3. Check if the product and shop data come from your shop's data.

Changelog entry

[puntope]

✅ LGTM

I tested locally and I see the title, logo and product

I also edited in a block theme and worked as well.