Redirect 404 when the suggestedEntityId content has been deleted for a content template

Overview

If a piece of content that is set to be used in the content template preview has been deleted, then clicking that template in the menu results in a 404 since the content no longer exists. The only way out of that is to remove the node from the URL, otherwise the page is stuck with a 404.

Aka /canvas/template/node/article/full/1 if I delete node 1 then clicking the template item again will result in a 404.

Proposed resolution

Handle 404 and redirect to /canvas/template/node/{bundle}/{viewMode} which will either re-route itself to the next existing suggestedEntityId or to the state where a user is shown the "No content available" screen with the button to create a new piece of content.

User interface changes