Standardize metadata type handling in `VoxelProvider`

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

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

```javascript
/**
* 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`:
```javascript
return {
className,
names,
types,
componentTypes,
minimumValues: hasMinimumValues ? minimumValues : undefined,
maximumValues: hasMinimumValues ? maximumValues : undefined,
};
```

As part of https://github.com/CesiumGS/cesium/issues/12297 we should simplify and improve documentation by using lists of property info objects, following the pattern of the metadata schema.