Tiles Traversal: Only load necessary tiles

[gkjohnson]

Related to #1344

• Add support for an optimized tile loading traversal that will only load tiles that need to be loaded. Based on on the Cesium Unreal traversal approach.
• Add "loaded" field to stats.

Algorithm TODO

• Add support for "kicking" to support zoom in without flashing
• Delete unused queued tiles (see #1422)
• Add support for "ancestor meets sse" logic for support zoom out without flashing
• Test with google tiles data set
• Correct handling of "ancestor meets sse" logic
• Ensure raycasting works as expected
• Allow for "trickle in" of tiles on initial load
• Investigate high number of active tiles vs typical traversal
• Add a "loadSiblings" option
• Understand why a low LoD tile loads initially
• Re-add matterport fix #1304
• Investigate weird raycasting / low lod tile here:
  • http://localhost:5173/three/googleMapsExample.html#lat=1.4056&lon=35.7235&height=1296.49&az=-3.31&el=-23.53&roll=-0.00
  • Happens because all children are outside the frustum so this gets hidden but is still active due to load siblings. Not much to be done I don't think
  • The flash occurs due to the child tileset being loaded
• Document limitations
  • shared caches and queues need to be shared by tiles using the same strategy
  • fade tiles does not work
  • any "virtual" or generated geometry will not work (quantized mesh splitting, overlay splitting)
• Validate that intermediate tiles do not load
• Understand the camera "jump" on reload
• Ensure additive refinement works as expected
• Clean up

Future

• Review dynamically generated / expanded tiles to ensure it works
  • These do not work since they only expand the children once the tile itself is loaded and disposed of once the internal parents are disposed.
  • That means we can get into an internal oscillation state when the parents are disposed, subsequently disposing of the children, causing that parent to render again.
• Add traversal utilities to improve readability of traversal algorithm
• Separate traversal variables into a dedicated object (related to Migrate more logic to core #1375)
• Ensure compatibility with broader plugins including fading & tile splitting (quantized mesh, overlays, related to #857)
• Make this the default and only traversal strategy once known to be stable
• Add delay to downloads / tile updates to prevent unnecessary downloads & data used (#1423)

[gkjohnson]

A comparison of this view:

	Geometry Tiles Loaded	Internal Tilesets Loaded	Total	Delta
master	340	77	417	0
optimized	254	77	331	86
no siblings	164	50	214	203

[gkjohnson]

cc @dbuck - with this change you will no longer be able to override the download and parse queue priority callbacks. I seem to recall you mentioning this is something you were doing previously but I'm not sure if you're still using that.