[HUBS] [Upcoming] GLTFLoader: Add loadNode hook

[HUBS]
This change is needed for glTF LOD support.
This change is not merged into the official Three.js but
likely it can get in soon.
mrdoob#25077
We can remove this commit if the PR is merged to the
official Three.js and upgrading our Three.js fork to the
one including the change.

Author: takahirox

examples/jsm/loaders/GLTFLoader.js

@@ -2540,7 +2540,11 @@ class GLTFParser {
 					break;
 
 				case 'node':
-					dependency = this.loadNode( index );
+					dependency = this._invokeOne( function ( ext ) {
+
+						return ext.loadNode && ext.loadNode( index );
+
+					} );
 					break;
 
 				case 'mesh':