Don't share geometry arrays between Batch and Primitive

[shunter]

Make a copy of the array of geometry instances before passing to the Primitive constructor.

In the batches, geometries is a live reference to the array inside the AssociativeArray, which is owned by the batch. We need to make a copy of the array so that subsequent changes to the batch don't affect the Primitive's view of the instances, which could happen during async creation or combining.

Fixes #5947

I marked this next release because the crash in #5947 is consistently affecting a customer application so I would like to get this looked at for 1.66.

[cesium-concierge]

Thanks for the pull request @shunter!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[shunter]

Here's the Sandcastle test case copied from #5947

var viewer = new Cesium.Viewer('cesiumContainer');

var entities = [];

var i;
for (i = 0; i < 100; ++i) {
    entities.push(viewer.entities.add({
        polyline: {
        positions : Cesium.Cartesian3.fromDegreesArray([-75, i/2,
                                                        -125, i/4])
        }
    }));
}

function removeEntity() {
  console.log(viewer.entities.removeById(entities[entities.length-1].id));    
}

var originalPrimitiveUpdate = Cesium.Primitive.prototype.update;

var updateCount = 0;

Cesium.Primitive.prototype.update = function(frameState) {
    originalPrimitiveUpdate.apply(this, arguments);
    
    if (updateCount === 0) {
        removeEntity();
    }
   
    updateCount++;
};

[mramato]

Thanks @shunter

Will look at this right now.

[mramato]

By right now, I mean this afternoon of course.

[mramato]

Reading the linked issue and trying to job my memory, but I can't think of a single reason we would ever have intentionally shared these arrays. I think making a copy is the right things to do here.

[mramato]

@shunter just to throw out another thought, would it make more sense for Primitive to copy during construction? I guess this is kind of a CesiumJS design decision we made a long time ago for performance reasons, we never copy arrays unless absolutely needed.

So if that's still the pattern we follow, I'll merge this. Just figured it was worth a separate comment first.

[mramato]

Update CHANGES

[shunter]

I thought about putting the defensive copy inside the Primitive constructor, but that would introduce an extra redundant copy in the numerous cases where we are passing a temporary array into the constructor.

[shunter]

I updated CHANGES.

[mramato]

Yeah, that's what I figured. Thanks @shunter!