Standardize metadata type handling in `VoxelProvider`

[jjhembd]

VoxelProvider is inconsistent with the rest of the repo in the way it handles metadata properties.

Metadata properties are specified in the tileset.json / schema.json as a list of objects:

"properties": {
  "property1": {
    "type": "SCALAR",
    "componentType": "FLOAT32"
  },
  "property2": {
    "type": "VEC2",
    "componentType": "FLOAT32"
  }
}

But in VoxelProvider these are flattened into arrays, as follows:

  /**
   * Gets the metadata names.
   *
   * @type {string[]}
   * @readonly
   * @constant
   */
  names;

  /**
   * Gets the metadata types.
   *
   * @type {MetadataType[]}
   * @readonly
   * @constant
   */
  types;

  /**
   * Gets the metadata component types.
   *
   * @type {MetadataComponentType[]}
   * @readonly
   * @constant
   */
  componentTypes;

While this structure may initially have been chosen for performance reasons, in the current code we only loop over properties once when loading a VoxelProvider, so performance benefits (if any) are minimal. Meanwhile, the flattened array pattern adds complexity in a few places:

• Looping over properties: we have to look up the name, type, and componentType of each property separately, assuming/hoping that the indices are consistent
• TS/JSDoc documentation for internal functions: a helper function that loops over properties has an awkward return type. See getAttributeInfo in Cesium3DTilesVoxelProvider:

  return {
    className,
    names,
    types,
    componentTypes,
    minimumValues: hasMinimumValues ? minimumValues : undefined,
    maximumValues: hasMinimumValues ? maximumValues : undefined,
  };

As part of #12297 we should simplify and improve documentation by using lists of property info objects, following the pattern of the metadata schema.