Use `Model` for `.vctr` and `.geom` contents

Right now, vctr and geom contents still use custom classes (Vector3DTileContent and Geometry3DTileContent).

This would involve:

1. Making VctrLoader to parse .vctr files and transcode to a ModelComponents instance, much like B3dmLoader does for .b3dm file
2. Similarly, make a GeomLoader for .geom files.
3. Add pipeline stages to Model as needed to implement any unique functionality
4. Check that picking/styling works with ModelFeatureTable instead of the old Cesium3DTileBatchTable

Ideally, at the end of this, nothing will use Cesium3DTileBatchTable (vctr and geom were the main stragglers), and we can consolidate that class with ModelFeatureTable to make things simpler.

Start by comparing the planned VctrLoader and GeomLoader with B3dmLoader, then trace how ModelComponents and Model pipeline stages handle the existing vctr and geom paths. Inspect picking and styling through ModelFeatureTable versus Cesium3DTileBatchTable. Done means both formats use Model, their unique behavior works, and the old batch table is no longer needed.