Add clipping planes to ModelExperimental

[j9liu]

Closes #10100.

This PR implements clipping planes in ModelExperimental, following how they are implemented in Model.js. Some sandcastles to test:

• modified ModelExperimental 3D Models
• modified Many Clipping Planes (ModelExperimental is second option in the dropdown menu)
• modified 3D Tiles Clipping Planes TODO: is crashing when enableModelExperimental = true
• Terrain Clipping Planes (not modified by changes but should still work)

Unit tests were added accordingly -- I realized I forgot to add a ImageBasedLightingPipelineStageSpec in my IBL PR, so it's included in these changes.

EDIT: also fixes #8234

[cesium-concierge]

Thanks for the pull request @j9liu!

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Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.

[ptrgags]

@j9liu in regards to that tileset that's crashing, it's due to the BIM model being a glTF 1.0 asset which is not currently supported.

Try This modified Sandcastle -- everything else is running fine.

However, I notice one thing that seems off. If you choose the Point Cloud example, the clipping planes widget's translation seems to move much faster than the mouse. Does this have to do with bounding spheres being too large? or something else? (#10244)

[j9liu]

@ptrgags it seems that the plane's translation is faster than the most whether ModelExperimental is used to load the Sandcastle or not. The original, unmodified Sandcastle demonstrates the same behavior

[ptrgags]

@j9liu had a few comments about the code, but the examples seem to be working correctly.

[ptrgags]

@j9liu, @lilleyse and I have been discussing this offline, not sure the best way we want to handle this. It would be nice to make clipping planes shareable, but that might require putting more responsibility on the user since it's hard to tell when to destroy the GPU resources.

See also #6599 (comment).

Not sure if this discussion has to hold up this PR (any changes could come later). just wanted to write it down somewhere.

[ptrgags]

We decided that it would be better to handle this with some sort of reference count mechanism. I'll write up the discussion in a separate issue and link it here.

[ptrgags]

Yesterday afternoon I opened #10257 for this.

[j9liu]

@ptrgags updated! I also pushed a change to fix #8234.

[ptrgags]

@j9liu everything looks good, and #10257 will be a separate PR so it doesn't need to hold this one up.

The Mount St. Helens example looks a lot better now!, it's easier to see the difference:

Without clipping Planes	With Clipping Planes

I checked that the Model sandcastles are working correctly with these changes and that the ModelExperimental versions are working properly aside from known issues (we also noticed #10255 along the way).

Thanks @j9liu, I'm merging!