Fix scaling problems in sixDofDragBehavior

[carolhmj]

Related forum issue: https://forum.babylonjs.com/t/unselected-meshes-move-alongside-the-selected-mesh/46627/11?u=carolhmj

The resetting/setting of the parent in _sceneRenderObserver seems to be causing some instability in the scale decomposition for nodes with parents and certain rotation/scales, so instead of doing this process (which is also more costly in performance terms), the idea is to do all the operations in the node's local space.

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

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[sebavan]

LGTM, I trust you on the maths :-) Let s merge after @Popov72 review

[Popov72]

Same for the maths :)

Maybe we can ping @CraigFeldspar as he is the original author of the behavior.

[CraigFeldspar]

Looks good to me, I just have a doubt on the fact that the delta vector is transformed as a position and not a normal