`EditableDatumLabel` uses `activate`/`deactivate` methods for showing or
hiding its widgets in the scene.
However, `activate`/`deactivate` methods can end up being called as part
of a scene graph / Coin action (`SoAction`) handler, in the context of
`SoFCUnifiedSelection`, and this ended up in a Coin warning and eventual
crash due to the scene graph being manipulated (nodes being removed),
which Coin has checks for in debug mode:
```
Coin error in SoGroup::removeChild(): tried to remove non-existent child
0x5555579c5290 (Annotation)
```
Fix this issue by using a `SoSwitch` node instead and by controling the
child visibility using it instead.
* Core: Add possibility for task dialogs to associate a view and be able to close when associated view is closed.
* TaskImage: Use task dialog view association.
* Sketcher: Use task dialog view association. Preventing crash (https://github.com/FreeCAD/FreeCAD/issues/16702)
* EditableDatumLabel: Use QPointer to prevent crash
