Sets up custom post types and Listing block prototype.

Instead of just registering a single Listing block and selecting the type in the parent post, this registers a separate block for each listing type (all of which use the same code).

Addresses pull request feedback and refactors post types config into a more DRY treatment.

This removes the Curated List CPT in favor of a wrapper block that can be inserted into any other post or page. This block can contain Listing blocks to create curated lists anywhere, and can be converted to a Reusable Block if it needs to be reusable.

Lays out a method of passing attributes data from the Curated List block to its child Listing inner blocks, without relying on contexts. We basically duplicate parent block attributes on each child block and sync the values of those attributes.

This establishes a pattern for providing block patterns for particular listings CPTs. This might let us provide structured content without having to register metadata fields for listing content.

Adds support for location-based data using the jetpack/maps block. If a listing CPT of any type contains a jetpack/map block with location data, the location data is used to show the listing on a map for any Curated List blocks containing the listing post.

Sets up a sync from certain content blocks to post meta fields. This will help us more easily implement search/filter functionality for listing posts on a large scale.

We want to avoid letting editors nest Curated Lists inside list items which could be nested inside Curated Lists which could be inside list items which could be... etc.

Moves shared styles to a `shared` SCSS folder and implements helpers to output the same class names in editor + front-end based on curated list block attributes.

- show author
- text color
- type scale
- all options reflected in both editor and front-end

Block patterns and block pattern categories can only be registered on init or admin_init hooks in WP 5.5.