Migrate more logic to core #1375
Description
Related to #1374, #1373, initial Babylon js implementation
In order to facilitate adding the loader in to other engines more logic from the three.js TilesRenderer can be migrated to the core implementation. Some ideas:
- Codify a dedicate field for necessary and per-engine pieces of data per tile (see the "cached" subfield in three.js version). This could require fields such as "scene" and "boundingVolume".
- The above should allow for events to implicitly fire a "scene" object that is currently used in TilesRenderer.
- If "boundingVolume" is required and shaped consistently then raycasting logic could be moved to core.
- Abstract handling of the "gltfUpAxis" behavior somehow.
- "calculateTileViewError" is probably the most complicated function to implement and could be broken up into multiple more simple functions to make this more simple.
- Relatedly, an abstract "camera" list could be maintained so the base class can iterate over them.
- Move more events to core.
- Move more update() function logic to core.