gate import on bevy_animation in bevy_gltf (#18403)

# Objective

- `collect_path` is only declared when feature `bevy_animation` is
enabled
- it is imported without checking for the feature, not compiling when
not enabled

## Solution

- Gate the import

crates/bevy_gltf/src/loader/mod.rs

@@ -66,6 +66,8 @@ use crate::{
     GltfMaterialName, GltfMeshExtras, GltfNode, GltfSceneExtras, GltfSkin,
 };
 
+#[cfg(feature = "bevy_animation")]
+use self::gltf_ext::scene::collect_path;
 use self::{
     extensions::{AnisotropyExtension, ClearcoatExtension, SpecularExtension},
     gltf_ext::{
@@ -75,7 +77,7 @@ use self::{
             warn_on_differing_texture_transforms,
         },
         mesh::{primitive_name, primitive_topology},
-        scene::{collect_path, node_name, node_transform},
+        scene::{node_name, node_transform},
         texture::{texture_handle, texture_sampler, texture_transform_to_affine2},
     },
 };