GLTF Mesh Import: Downloaded models are giving a Missing required level of detail until re-exported

[AtlasLinden]

Environment

Second Life Project Gltf-mesh-import 7.1.14.15119648860

Description

A mesh is downloaded from Sketchfab and after clearing settings on the Upload Model floater (due to #4105), an error pops up stating "Missing required level of detail.
https://gyazo.com/5cd7608619587c11dde88cc98baad0bc

If the same model is imported then exported via Blender, the error only appears momentarily.
https://gyazo.com/a3b1a707308364ef8e0d6c034da7094d

The model used in the clips above: https://sketchfab.com/3d-models/cute-eagle-4575a75b8cc4427d87197fa86cd8c981 (1k GLB)

Reproduction steps

1. Download the above model
2. Attempt to upload it via Build>Upload>Model (May need to select "clear settings" button in the floater.)

[AtlasLinden]

Another model this reproduces for that may not require first clearing Upload Model settings: https://sketchfab.com/3d-models/2023108-head-of-apollo-8ac05adbe3de41a3bde5c5cbee296b50 (1K GLB)

[maxim-productengine]

Both models (cute_eagle.glb and 2023.108_head_of_apollo.glb) use deprecated "KHR_materials_pbrSpecularGlossiness" extension, which we don't support.
So, we may try to convert from the specular/glossiness to the default metallic/roughness instead of just failing upload.

[aiaustin]

Perhaps just ignore any unimplemented, deprecated or obsolete PBR (KHR_material) properties to make the upload robust.

Ditto for some validation errors like metallic properties being outside the range 0..1. I see a NASA mesh (Perseverance Rover) that has metallic set to 1.000001 or something silly like that.

[maxim-productengine]

So, for now we're ignoring unsupported extensions (warning msg will be added to Log tab).
This way the mesh will be uploaded, but not the expected materials.

[AtlasLinden]

Passed QA.
Verified on Second Life Project 7.1.14.15312236431 (GLTF Mesh Import) on Win11/MacOS
The above models can now be uploaded immediately without any need to re-export from elsewhere.
The log provided can be observed in image below. Note that the exact extension information is not provided. A separate issue has been created for this: #4190