Blender Git Loki

Multi-Object-Editing: MESH_OT_separate by Nick Milios

Patch description:

- Reports "Nothing selected" only when all objects has no selection
and it is in Separate type(Mode)
- Tested all types (Seperate/By Material/By loose parts)
- Instead of using

```
BKE_view_layer_array_from_objects_in_edit_mode_unique_data
```

I used

```
BKE_view_layer_array_from_bases_in_edit_mode_unique_data
```

Because it needs the "Base" not the "Object" itself.

Maniphest Tasks: T54643
Differential Revision: https://developer.blender.org/D3267