Why limit to admin theme?

Problem/Motivation

I wonder why you would limit this to the admin theme. I am uploading a patch which allows selecting any enabled theme for use with Layout Builder.

My use case (which this doesnt help) was that i am using a site theme which is based on Bootstrap 3. Layout Builder does not work well with BS3. So i found this module. This module helps a bit but as site admin theme is not BS based; the layout of the page is lost when not using BS theme. So i had the idea: what if i could pick any theme and select a BS4 or BS5 theme (as they do work properly with LB) to use just for LB.

It turns out my use case isn't helped by this change as the layouts are specifically BS3 and LB does not display them correctly with a BS4/5 theme.

But, since i had already written the code to try this.. i'll post the patch here in case someone has a different use case which this does help.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes