`Model` - support `noData` and `required` from `EXT_mesh_features`

One of the schema changes from EXT_mesh_features is to remove default and optional from the schema and replace them with noData and required. The CesiumJS implementation still needs to be updated for this.

This was out of scope for #9880 since it has wider reaching implications. I want to wait on this until getting metadata working in Custom Shaders

[jjhembd]

A significant part of what this issue describes has been implemented in #10520 and #10683.

I opened two new issues, #10799 and #10800, to better define the remaining features that have not yet been implemented.

[ptrgags]

@jjhembd There are some parent pointers that you can use to locate the tileset:

• renderResources.model is like a parent pointer that points upwards a few levels of abstraction to the ModelExperimental to which this primitive belongs
• model.content gives you a pointer to the ModelExperimental3DTileContent, but this is only defined for 3D Tiles (if this was an individual model loaded from ModelExperimental.fromGltf(), this will be undefined)
• content.tileset is a pointer to the containing tileset.
• from there you can access tileset.metadataExtension.statistics as described above. If it’s present, then yes add it to the metadata struct.

These pointers skip over a few levels of abstraction. To recap the full hierarchy here (from root to leaves):

• Cesium3DTileset
• One or more levels of Cesium3DTile (a tree navigated via the tile.children array)
• A Cesium3DTileContent (interface), in this case ModelExperimental3DTileContent
• ModelExperimental
• ModelExperimentalSceneGraph and other abstractions
• the draw command building pipeline, which in this case receives a PrimitiveRenderResources