Search: use mshots for expanded/grid results that don't have images

I'm uncertain about this solution, but there is at least one case it would help.

https://dotcompatterns.wordpress.com/ has all the wpcom block patterns. They are implemented as blocks so there is no image for us to show and we really can't take the content and render them in results. That means that the results look like this:


When the main page is this https://dotcompatterns.wordpress.com/2020/06/16/audio-player/

What if when there is no image url we just use an mshot url of the page the link goes to. e.g. a result for the Google homepage would have this image next to it: https://s0.wp.com/mshots/v1/http://google.com?w=500

It may make the results look a lot better. An image is worth a thousand... This may also improve our search results for products or mixed products/articles.

More mshots info:
- a8c FG
- https://github.com/Automattic/mShots

cc @jeffgolenski

Start by reviewing the issue's example results, the mShots reference, and the Automattic/mShots project linked in the description. Done should mean deciding whether missing-image expanded or grid results should use an mshots URL and documenting the expected behavior for those results.

Written by the indexing model from the issue text.