doc: Sync classref with current source

Move EditorSceneImporterFBX doc to its module folder.

modules/fbx/config.py

@@ -4,3 +4,13 @@ def can_build(env, platform):
 
 def configure(env):
     pass
+
+
+def get_doc_classes():
+    return [
+        "EditorSceneImporterFBX",
+    ]
+
+
+def get_doc_path():
+    return "doc_classes"