Library sections preview using default theme

Problem/Motivation

It would be great to have the possibility of preview each section using main theme instead of the admin one as in cannonical entity route & showing rendered "layout_section" as it would do when imported in layout builder content design page.

Implemented into section library module as it provides library feature, keeping this as related just in case an iterarion is needed (also independent in case). Also in case anyone search related into vlsuite issues.

Apply related section library issue MR patch changes in your project if you need it.