Add tile loading events for Voxels

[lukemckinstry]

Description

Takes the following events from Cesium3DTileset and adds them to VoxelPrimitive

• allTilesLoaded
• initialTilesLoaded
• loadProgress
• tileLoad
• tileUnload

Also makes VoxelPrimitive use Cesium3DTilesetStatistics class, but only makes use of 2 of the stats in the class so far.

ToDo

• Did not carry over these event types
  • tileFailed - issues described in this comment Voxel API should conform to Cesium3DTileset interface #12297 (comment)
  • tileVisible - not sure is there is an equivalent to selectedTiles (from Cesium3DTileset) in VoxelPrimitive, if so I believe this would be simple.
• Still need to add tests, but these look straighforward to carry over from Cesium3dTilesetSpec to VoxelPrimitiveSpec.
• move code to call events out of VoxelTraversal.printDebugInformation.

Issue number and link

related to #12297

Testing plan

Many events currently fire inside of VoxelTraversal.printDebugInformation. Enable this but comment out the last line of the function which logs the debug output so you can read the output from listeners you set up to listen to the new events.

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @lukemckinstry!

✅ We can confirm we have a CLA on file for you.