Create a Drupal-rendered block fallback React component

Background

In 5) Create a discovery mechanism to associate a block plugin with a React component) we will convert InlineBlock to React.

But there are many other Block plugins in Drupal.

In this scenario, we'll need a fallback plugin to provide the user with a reasonable preview. This will bridge the Decoupled layout builder and Block types that need to be converted.

Proposed resolution

Create a fallback React block plugin component that can request Drupal for rendered previews. Extend the persistence layer to add another Route for this.

Out of scope but for future consideration:

• Support a legacy configuration form for these blocks as well