Add bevy_fbx, an FBX loader based on ufbx

[VitalyAnkh]

Objective

• Support FBX asset loading via ufbx
• Fixes Support FBX file loading #15705

Solution

• Add bevy_fbx, an FBX loader based on ufbx.
• Why using ufbx? It is a thoroughly tested, single-file FBX loader that now powers Godot’s native FBX importer and Blender’s new official importer; it also ships with first-party Rust bindings.

Testing

• example load_fbx, asset_loading.

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[mockersf]

as it uses a native dependency, I don't think it should be part of the default features

[pcwalton]

Agreed with @mockersf. FBX support would be very nice, but C++ dependencies add a lot of pain to the out-of-the-box experience in many cases, so let's make it opt-in.

[github-actions]

The generated examples/README.md is out of sync with the example metadata in Cargo.toml or the example readme template. Please run cargo run -p build-templated-pages -- update examples to update it, and commit the file change.

[VitalyAnkh]

ufbx is a self-contained FBX loader made up of just two files—ufbx.c and ufbx.h. It depends only on libc and has no other significant prerequisites, so it’s much simpler to build than most C++ or Rust libraries. That said, I’m happy to make FBX support an optional feature if that’s the community consensus.

[github-actions]

You added a new feature but didn't add a description for it. Please update the root Cargo.toml file.

[IceSentry]

I know it's still WIP, but it would be way easier to review if the main load() function was split into multiple functions. A bit like how bevy_gltf has load_materials, load_image, load_node, etc.

Also, once the PR is ready to merge I think it should only have one .fbx file in the asset folder. It's a good feature to have but we need to keep the size of the repo in check.

[VitalyAnkh]

I will refactor the main load() function following bevy_gltf. And there will be only one cube.fbx file in the repo, and I have already added a scene_viewer_fbx example to inspect other fbx files easily. Thanks for the nice advice!

[github-actions]

You added a new feature but didn't add a description for it. Please update the root Cargo.toml file.