Support glTF EXT_mesh_primitive_restart in CesiumJS

[markschlosseratbentley]

See iTwin/itwinjs-core#8312 on iTwin.js. This was recently merged in and supports the proposed EXT_mesh_primitive_restart glTF extension.

We could consider adding similar support in CesiumJS. Reference the above two links as this work is considered.

[javagl]

Assuming that this can be closed as of #12792