Add "Show Skeleton" option to the advanced import settings dialog 3D preview

[LordMcMutton]

Describe the project you are working on

Exporting a main GLTF file with the skeleton and mesh, and bringing in additional animations via GLTF files with only the skeleton and specific Action tracks

Describe the problem or limitation you are having in your project

This method not using the mesh means that you can't ensure that the animation pipeline worked as intended without exporting the mesh to check, then doing it again without the mesh, or putting in all of the Animation Slice data to check, setting it up in the Editor, and checking if its working on the main model.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Being able to see the Skeleton setup in the Advanced Import window will improve this method's workflow by allowing the user to confirm everything is working properly before moving on to the next steps

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

A few options:

-Have it on all the time, which might make models with the mesh included difficult to see
-Have it check if a mesh exists and, if not, make the Skeleton visible
-Add a checkbox in the 'Actions...' menu
-Add a checkbox somewhere else on the Advanced Import menu

If this enhancement will not be used often, can it be worked around with a few lines of script?

Not to my knowledge

Is there a reason why this should be core and not an add-on in the asset library?

Enhancement to an existing system

[Calinou]

Thanks for the proposal! Consolidating in #6801. This feature is implemented in the upcoming 4.4 (try it in 4.4.dev7).