Skinned Mesh Renderer Bounds aren't calculated.

### Describe the bug 💬

This is inconsistent with FBX importer. Causes redundant prefab modifications to be to be applied in the scene (or in prefab variant).


### Steps to reproduce 🔢

Select a skinned mesh renderer in an imported GLTF asset and see the bounds are zero.

### Files to reproduce the issue ♻

_No response_

### Editor Version 🎲

Other (Provide details below)

### Render Pipeline and version

Not relevant

### UnityGLTF Version

2.17.1

### Operating System 👩‍💻

Windows

### When does this problem happen?

- [x] Editor Import
- [ ] Runtime Import
- [ ] Editor Export
- [ ] Runtime Export

### Additional Info 📜

_No response_

### Validations 🩹

- [x] I have [searched existing issues](https://github.com/KhronosGroup/UnityGLTF/issues): no issue already exist that reports the same problem.
- [x] I follow the [Code of Conduct](https://www.khronos.org/about/code-of-conduct)
- [x] I provided a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example), including files when necessary.

No source file or test is identified. First reproduce the issue in UnityGLTF 2.17.1 by selecting a SkinnedMeshRenderer in an imported glTF asset and compare its bounds with the FBX importer. Done means the imported bounds are calculated and redundant prefab modifications are no longer required.

Written by the indexing model from the issue text.