Research (and implement if feasible) rendering all 3D view in just one QQuickView internally

Currently 3D view renders the main scene (now shown but needed for intializing things properly) and the actual 3D editor scene in separate QQuickViews (windows). Various material and node previews are also rendered in separate windows. This causes issues with sharing various things on quick3d side, which often limits sharing to a single window. For example, 2D items inside 3D scene cannot be shared without significant overhaul of rendering engine.

Investigate the possibility (and implement if feasible) of rendering everything in a single QQuickView.