Scale parameter should be removed from Robot node

[ad-daniel]

Describe the Bug

The Robot node inherits the scale parameter from the Transform node, using this parameter however has several issues/bugs:

• If a user sets the density in the Physics, it will scale but if it sets the mass, it doesn't.
• If the robot has sensors, like a distance sensor. After scaling it won't work well anymore. (detection point is incorrect, lookup table isn't respected, ...)
• Although it might be possible to "fix" all sensors to work with a smaller uniform scale, for non-uniform ones such as scale 0.5 1.5 0.3, it would be incredibly hard to have the desired behavior for every sensor type

[omichel]

I believe the scale parameter should be allowed only in the Transform node and in no other node, as it will cause various problems. Even in a simple Solid node, there is a problem if the mass is specified in the Physics node of the Solid as its value won't scale or won't be correct. Also, for the same reason, Transform nodes shouldn't contain any Solid node (or descendant). When needed, users should use an upper Solid node (instead of a Transform) to encapsulate other Solid nodes.

[omichel]

An idea to make things clean would be to introduce a Pose node that would be basically like a Transform, but without the scale field. The Solid nodes would then inherit from Pose and a Pose node would be allowed to include solid children.