Fix entity visibility for non-dynamic show

[hpinkos]

Fixes #7132

Updating the show property has a special case if show is constant. Instead of checking the value of the attribute every frame, we listen for changes to the isShowing property and update the attribute value without creating a new primitive. The the old polygon was showing when the new polygon was added because we reused the geometry instance that still had the old attribute value when the new primitive was created with both geometry instances.

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

var greenPolygon = viewer.entities.add({
    polygon : {
        hierarchy : Cesium.Cartesian3.fromDegreesArray([-108.0, 42.0,
                                                        -100.0, 42.0,
                                                        -104.0, 40.0]),
        material : Cesium.Color.GREEN,
        height: 0
    }
});


Sandcastle.addToolbarButton('Hide', function(){
    greenPolygon.show = false;
});

Sandcastle.addToolbarButton('Add polygon', function(){
    viewer.entities.add({
        polygon : {
            hierarchy : {
                positions : Cesium.Cartesian3.fromDegreesArray([-108.0, 33.0,
                                                                -100.0, 33.0,
                                                                -104.0, 35.0]),
            },
            material : Cesium.Color.RED,
            height: 0
        }
    });
});

[cesium-concierge]

Thanks for the pull request @hpinkos!

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[hpinkos]

I tested to make sure this didn't introduce a regression for any of these cases: #7053 #7048 #2909 #4714 #6830 #5371

[mramato]

This all sounds vaguely familiar to me, but do we know when this regression happened? This is just putting back old behavior, right?

[mramato]

git bisect points to 6d11d0f as the first bad commit. Does that change how this should be fixed at all?

[hpinkos]

This is a better fix than the old behavior because it specifically addresses changes to show for static geometry. The code from that commit you mentioned was removed because it was causing problems for dynamic geometry #7048

[mramato]

Sounds good. Can we add unit tests?

[hpinkos]

Thanks for pushing back on this @mramato! I assumed we didn't have many unit tests for things like this because they were difficult or impossible to write, but it was actually pretty straight forwards. This is ready now

[mramato]

You have some failing tests

[hpinkos]

@mramato this should be ready now

[mramato]

Travis builds are down while GitHub is still recovering from earlier failure. So I'll have to test this locally but will merge if there aren't any problems.