GDT: Make tolerance optional

[adamchalmers]

The distance/dimension gdt function should not have a hard requirement for a tolerance arg. This is what GD&T is for- to describe the required accuracy of a feature without having to add a tolerance to every dimension.

If tolerance is not sent, no tolerance should be shown. In other words, the leader in the scene should show only the dimension value.

[codecov]

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[adamchalmers]

OK this is what you get if you set tolerance to 0.

vs. setting tolerance to 0.1mm:

So some parts of the engine already support making the tolerance optional. Hopefully this will just be plumbing the data around and not need big changes.