Voxel Spec data uses legacy 3D Tiles 1.1 representation

[javagl]

The spec data for the Voxels uses subtree files with contentAvailability. The latest version of the specs, this should actually be an array.

(The fix should be trivial, and CesiumJS supports the legacy version, so this is not criticial, but this issue is rather intended as a note (maybe for myself) to fix this when there's a bit more time)

[Vamonosraza]

Hi. I am with JTC. I believe it was said to make a comment if we want to work on an issue. This seems like a good one for me to geting familiar with the cesium environment!

[Vamonosraza]

Hey, what am I missing?