What?

This PR replaces a get_comments() call and database query with get_comments_number().

Why?

This approach has three advantages:

1. It's faster. get_comments_number() uses a post property vs a separate database query.
2. get_comments_number() is filtered, and it's much easier for plugins/themes to manipulate, vs having to use pre_get_comments and jump through several hoops.
3. This is consistent with the way core themes used to determine whether or not to render the comments template, from twentyten up to twentytwentyone. Maybe even older, I didn't check Kubrick 😄.

Testing Instructions

Using the comments block under normal circumstances, no behavior changes should be observable.

To disabled comments and commenting on all content, one should now be able to:

add_filter( 'comments_open', '__return_false' );
add_filter( 'get_comments_number', '__return_zero' );

Observe that prior to this PR, comments will still render using the comments block.

Closes #48975