Centralized place for isSupported checks

`isSupported` checks are all over the place and not always consistent.
* Static functions on the file - `PointCloudShading.isSupported`
* Part of Entity - `Entity.supportsMaterialsforEntitiesOnTerrain`, `Entity.supportsPolylinesOnTerrain`
* Part of a Scene instance - `scene.pickPositionSupported`

Would it be better to have a centralized place for these checks?

Start by comparing the existing isSupported checks named in the issue: PointCloudShading.isSupported, Entity.supportsMaterialsforEntitiesOnTerrain, Entity.supportsPolylinesOnTerrain, and scene.pickPositionSupported. Determine whether a centralized location can cover these different ownership patterns and define what consistent behavior would mean. Done requires an agreed design and corresponding updates across the affected checks.

Written by the indexing model from the issue text.