Performance drops and QtDS becomes unresponsive when there's a lot of items in navigator

QtDS becomes really slow and unresponsive when editing components that have a lot of meshes and items in the navigator.

In the attached example project, scrolling the navigator in the "engine" component jumps the CPU consumption to 70%, and selecting an item in the navigator jumps the CPU consumption to 100% on a 6-core intel i7.

At this stage the tool becomes unresponsive, and it takes several seconds to select an item. It seems that more items there are in the navigator, the more severe this issue becomes.

This bug prevents working on projects that have 3D models with high mesh counts.

Steps to reproduce:
1. Download "WoW" project from https://git.qt.io/tetammin/wow

2. Open project and go to "ElectricEngine_WholeEngine.qml" component

3. Try to scroll in navigator and select meshes.

4. Same issue appears but on a smaller scale on other components, like the "car.qml"

Tested on 3 computers using Linux, Mac, and Windows. 

Video of issue: https://qtcompany.sharepoint.com/:v:/s/Automotivedemos/EUen6K8Zl9pBr6Db_NadTcsBp5_XutsxJnxa9ojyHB_bPg?e=fuxgB0