Instanced models are not being cached correctly between different ModelInstanceCollections

[lilleyse]

If multiple i3dm tiles are loaded, they all use the same Model cache key which is causing tiles not to render.

[lilleyse]

Quick update: I'm only seeing the wrong behavior for certain models. This leads me to believe it's not related to the cache key but instead something with the shader transformations.

[pjcozzi]

I don't know what it could be with the shader; only the program should be cached, not the uniforms (which is where I expect the culprit would be).

[lilleyse]

This was a problem in the instanced model conversion step, not in Cesium.