Use rel for cartographic polygon

[corybarr]

Resolves #639
Fixes #632

Based on the plan to add the CesiumCartographicPolygonPrim back into the codebase once the issue with BasisCurves inheritance is fixed, these are the minimal set of code changes to achieve removing the prim. To the end user, the "cartographic polygon" concept and terminology still exists. The term is still used in the UI. The only difference to the end user once the prim is added back should be the type of the prim in the Stage Window.

This means that OmniCartographicPolygon still exists, even though there is no corresponding USD prim.

Test file: noCartographicPolygon.clippingTest.TwoOverlays.usda.zip

[r-veenstra]

I've been testing and appears to be working as expected. All I could probably suggest is a warning to the log if a user links a basis curve without a globe anchor (something I've already done by accident).

[corybarr]

I've been testing and appears to be working as expected. All I could probably suggest is a warning to the log if a user links a basis curve without a globe anchor (something I've already done by accident).

I can see the use of that. Let's create an issue during standup if we want to. I think our rel workaround is good as workarounds go, but ultimately we should inherit from a BasisCurves so we can define the GlobeAnchor requirement in the schema. So any warnings would be temporary with an issue that keeps us from forgetting to remove them in the future.

[lilleyse]

Looks great! Nothing from me.