Add list of supported KHR extensions to bevy_gltf's docs (#19100)

# Objective

- Fixes #15068

## Solution

- Docs!

## Testing

I created this list by browsing Bevy's source code rather than testing
gltf files so its possible there is some partial/wonky support I didn't
uncover.

Author: jf908

crates/bevy_gltf/src/lib.rs

@@ -89,6 +89,43 @@
 //! Be careful when using this feature, if you misspell a label it will simply ignore it without warning.
 //!
 //! You can use [`GltfAssetLabel`] to ensure you are using the correct label.
+//!
+//! # Supported KHR Extensions
+//!
+//! glTF files may use functionality beyond the base glTF specification, specified as a list of
+//! required extensions. The table below shows which of the ratified Khronos extensions are
+//! supported by Bevy.
+//!
+//! | Extension                         | Supported | Requires feature                    |
+//! | --------------------------------- | --------- | ----------------------------------- |
+//! | `KHR_animation_pointer`           | ❌        |                                     |
+//! | `KHR_draco_mesh_compression`      | ❌        |                                     |
+//! | `KHR_lights_punctual`             | ✅        |                                     |
+//! | `KHR_materials_anisotropy`        | ✅        | `pbr_anisotropy_texture`            |
+//! | `KHR_materials_clearcoat`         | ✅        | `pbr_multi_layer_material_textures` |
+//! | `KHR_materials_dispersion`        | ❌        |                                     |
+//! | `KHR_materials_emissive_strength` | ✅        |                                     |
+//! | `KHR_materials_ior`               | ✅        |                                     |
+//! | `KHR_materials_iridescence`       | ❌        |                                     |
+//! | `KHR_materials_sheen`             | ❌        |                                     |
+//! | `KHR_materials_specular`          | ✅        | `pbr_specular_textures`             |
+//! | `KHR_materials_transmission`      | ✅        | `pbr_transmission_textures`         |
+//! | `KHR_materials_unlit`             | ✅        |                                     |
+//! | `KHR_materials_variants`          | ❌        |                                     |
+//! | `KHR_materials_volume`            | ✅        |                                     |
+//! | `KHR_mesh_quantization`           | ❌        |                                     |
+//! | `KHR_texture_basisu`              | ❌\*      |                                     |
+//! | `KHR_texture_transform`           | ✅\**     |                                     |
+//! | `KHR_xmp_json_ld`                 | ❌        |                                     |
+//! | `EXT_mesh_gpu_instancing`         | ❌        |                                     |
+//! | `EXT_meshopt_compression`         | ❌        |                                     |
+//! | `EXT_texture_webp`                | ❌\*      |                                     |
+//!
+//! \*Bevy supports ktx2 and webp formats but doesn't support the extension's syntax, see [#19104](https://github.com/bevyengine/bevy/issues/19104).
+//!
+//! \**`KHR_texture_transform` is only supported on `base_color_texture`, see [#15310](https://github.com/bevyengine/bevy/issues/15310).
+//!
+//! See the [glTF Extension Registry](https://github.com/KhronosGroup/glTF/blob/main/extensions/README.md) for more information on extensions.
 
 mod assets;
 mod convert_coordinates;