Use `@namespace` in addition to `@enum` for jsdoc

## Old
When using the `@enum` tag by itself it puts the documentation in the global section and omits static functions on the enum. It's cluttered and missing information.


## New
By adding the `@namespace` tag it creates a new page for the enum and show the static functions:

---

Here's how the fix would look for `VoxelShapeType`:
```
/**
* An enum of voxel shapes supported by EXT_primitive_voxels. The shape controls
* how the voxel grid is mapped to 3D space.
*
* @namespace
* @enum VoxelShapeType
*/
```

One way to go about fixing this for all enums is to:
- Run `npm run generateDocumentation`
- Go to `http://localhost:8080/Build/Documentation/global.html`
- Add `@namespace` to every enum until there are no more in the global section

Also, update https://github.com/CesiumGS/cesium/tree/main/Documentation/Contributors/DocumentationGuide with information about enums / namespace.

Run `npm run generateDocumentation` and inspect `http://localhost:8080/Build/Documentation/global.html` to identify enums still documented in the global section. Add `@namespace` to those enum comments, then update `Documentation/Contributors/DocumentationGuide` with the enum and namespace guidance. Done means the enums have dedicated documentation pages with their static functions shown.

Written by the indexing model from the issue text.