When demo_mode, limit component list to only SDCs, not blocks

I searched the issue queue for , but no matches. I want every demo mode restriction to point to an issue that will lift that restriction. So, created the necessary issue: 📌 [Needs design] Library confusingly lists SDC-sourced and Block-sourced Components together Active .

Also started documenting the list of restrictions.

Left some minor nits

We are not doing this anymore, hence closing as outdated.