Remove ClippingPlaneCollection.clone

[hpinkos]

The presence of ClippingPlaneCollection.clone was causing a new ClippingPlaneCollection to be created every frame when it was the value of a ConstantProperty for a ModelGraphics.
This is also why we had to do this crazy CallbackProperty thing in the model clipping planes Sandcastle example.

None of our other collections like BillboardCollection and PrimitiveCollection have a clone method, and we weren't using it anywhere in our code, so I thought the best thing to do is remove it. I made it a breaking change instead of deprecating it because I don't think many (if any) of our users were using this function either.

[cesium-concierge]

Thanks for the pull request @hpinkos!

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[hpinkos]

@mramato can you review please?

[mramato]

@ggetz or @likangning93 are more familiar with this code, so they should probably be the ones to review. We should make sure there wasn't a good reason as to why this was added in the first place.

[hpinkos]

@ggetz can you review?

[ggetz]

clone was there because the content of every model used to share the clipping plane collection's list of planes, but needed to apply their own modelMatrix transform, but we moved away from that in #6201.

I agree the breaking change should be fine, I doubt many people are using that function, if any.

[ggetz]

The edge styling toggle no longer works on model entities, and after testing, I think the modelMatrix property of the tile content is not getting assigned correctly as I thought. Try lowering the SSE on the tileset so more tiles are loaded.

[hpinkos]

@ggetz The model thing is already a bug in master, the bug of creating an new clipping plane collection every frame in ModelVisualizer just happened to make it work for model entities. I wrote up this issue: #6878
I can start looking at it, but if you have any suggestions for how to fix it that would be appreciated.

I'm not sure what problem you found related to tile content, but I really don't think that's related to this PR since clone wasn't being used anywhere for the 3d tiles clipping stuff. Can you check to see if that exists in master as well?

[hpinkos]

Nevermind, I had a typo. I'll figure out what's going on with the model

[hpinkos]

Oh good, it's just a bug in the sandcastle example

[hpinkos]

@ggetz anything else?

[ggetz]

Thanks @hpinkos The model edge clipping is resolved!

However, there's still a problem with tilesets. If I chose the BIM model and use maximumScreenSpaceError : 2, I can see the smoke stacks aren't getting clipped correctly, however the edges are still highlighted in the correct places. Maybe this is an issue with discard in the shader? Are you seeing the same?

[hpinkos]

@ggetz opened #6879

Anything else?

[ggetz]

Other than that, this looks good. Thanks @hpinkos !