[For v0.19]Link: stage one, context aware selection
Created by: realthunder
- Major change in 3D selection/preselection to handle Coin node sharing
- Retiring SoFCSelection mouse handling in favor of SoFCUnifiedSelection
- Added picked list support to Gui::Selection for multi-element selection
Forum link: https://forum.freecadweb.org/viewtopic.php?f=17&t=23419