GLTF Mesh Import: Provide unsupported extension info in log

[AtlasLinden]

Environment

Second Life Project 7.1.14.15312236431 (GLTF Mesh Import)

Description

When uploading a model that uses unsupported extensions a warning message is given in the Upload Model floaters Log tab as per the fix from #4107

This warning states that an unsupported extension is being used but doesn't say which exact extension/s is giving the error. This information should be provided to the user in the Upload Model floater log so that they are immediately aware of the unsupported extensions and can provide any necessary changes to their model.

Note that the exact extension does appear to already be mentioned in SecondLife.log.
LL::GLTF::Asset::prep : Unsupported extension: KHR_materials_pbrSpecularGlossiness

Reproduction steps

1. Upload the following model: https://sketchfab.com/3d-models/cute-eagle-4575a75b8cc4427d87197fa86cd8c981 (1k GLB)
2. Observe Log in Upload Model floater

[Dan-Linden]

The unsupported extension is mentioned in the Log tab, but I no longer see it in the SecondLife.log
This message should show up in the SecondLife.log as well.

Failed QA.
Tested on Second Life Project Gltf Mesh Import 7.1.14.15361077240 on Win11 in the scope of https://github.com/secondlife/iqa/issues/504

[AtlasLinden]

The same behaviour as the previous comment that failed QA is observed.
That is, the unsupported extension information is mentioned in the Upload Model floater log but not SecondLife.log.

Tested on Second Life Project 7.1.14.15976006598 (GLTF Mesh Import) on Win11/MacOS

[AtlasLinden]

Log now mentions info such as the following:
LLGLTFLoader::notifyUnsupportedExtension : Model uses unsupported extension: KHR_materials_pbrSpecularGlossiness

Passed QA.
Verified on Second Life Release 7.2.0.16356654553 (2025.05) on Win11/MacOS

Tested on multiple different models. If new unsupported extension info is ever not provided, a new ticket can be filed.