Dropzone flickering

Problem/Motivation

When starting on an empty DB with builder and layers (and tree when dropable) on main, the first drop in a component slot trigger flickering and can fail.

It seems related to the main tabs pane being visible or not. And the fact that the dorpzone are created with the same group id in SortableJs.

Steps to reproduce

Start empty builder with main island builder and layers, drag a component with a slot.
Drag a block token : flick

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes