ScaleTool should ensure that the segment names for all Scales are the names of bodies

[tkuchida]

Comment from @chrisdembia on #1994:
"the scale tool should validate the segment names for all Scales to make sure they are the names of bodies, and not the names of PhysicalOffsetFrames, etc., which can't have scale factors."

[tkuchida]

Related: #1918

[chrisdembia]

Thanks for creating this.

[tkuchida]

@chrisdembia also suggested converting ScaleSet into a vector (e.g., of type Vec3 or std::pair<bool, Vec3>) so that scale factors can be retrieved directly using the Body's mobilized body index rather than repeatedly performing string comparisons with all the segment names in the ScaleSet.

[chrisdembia]

Ah I hadn't thought of that but I like that idea. That's better than using an sd::unordered_map<Body*, Vec3>, which is what I was thinking.

[aymanhab]

I'd be extra careful with introducing new containers across the interface that may cause issues for wrapping, scripting. Just a headsup

[chrisdembia]

I think this would be an internal cache.

[tkuchida]

Preprocessor should also check that scale factors are in the open interval (0, infinity).