Issue #2958727: Fix missing route and adjust new entity options.

Since not all entities follow the same route pattern (such as the Shortcut entity), fix the ‘route does not exist’ error by whitelisting a few popular entity IDs that are known to provide a route that works with our route pattern.

Move entity options under “entities” in addtoany.settings.yml, and update references.

Update admin CSS to style the layout of hyperlinks that link to the “Manage display” page for entity bundles.

Add 2 helpful notes in the Entities section.

Fix minor code style issues.