Use collection.featured_image instead of image

[martinamarien]

Why are these changes introduced?
Currently, the collection card only displays the collection image, if one exists.
In other themes, we use the collection's first product image as a fallback, if one exists.
Fixes #172

What approach did you take?
We recently introduced the new featured_image property on the collection object.
By using this property, it means:

• If a collection has a featured image, it will be used in the collection card
• If a collection has no featured image and the first available product has featured media, use the product’s first available featured media as the collection card image. (Collection: test collection)
• If the collection and its first product has no media, then do not show an image in the collection card. (Collection: shop all)

This PR converts collection.image to collection.featured_image in three places:

• Collection list template
• Collection list section
• Collection block in the collage section

Other considerations
N/A

Demo links
See test store

Testing and reviewing

• Please ignore online store git commits - I will revert when reviewing is complete
• Test:
  • Collection list template
  • Collection list section
  • Collection block in the collage section

Checklist

• Followed theme code principles
• Linted with Theme Check
• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility

[Al-Campuzano]

LGTM! 🚀

[tauthomas01]

Tested and looks good.

[KaichenWang]

Looks good!

[tyleralsbury]

Looks good. Love when something already exists for an elegant solution.

[tyleralsbury]

Suggested change

	{% endschema %}
	{% endschema %}