Add ufbx for FBX importing

This update introduces a new import method for FBX files using ufbx. If the fbx2gltf import fails, it will use the most recently cached scene from the ufbx import. The process is sped up by introducing threads to load the ufbx portion.

Key changes include:

- Support for importing geometry helper nodes in FBX files.
- Addition of cameras and lights with updated names.
- Removal of the fbx importer manager.
- Introduction of ModelDocument3D and updates to its methods.
- Changes to FBX import options and visibility.
- Updating the documentation and handling some errors.
- Store the original non-unique node, mesh and animation names in FBX and glTF.

Co-Authored-By: bqqbarbhg <bqqbarbhg@gmail.com>

misc/extension_api_validation/4.2-stable.expected

@@ -204,3 +204,14 @@ Validate extension JSON: Error: Field 'classes/Window/methods/has_theme_stylebox
 Fix the default parameter value for StringName and Variant.
 The changes to StringName parameters should be equivalent to the previous default values.
 The change to the Variant parameter in 'add_code_completion_option' breaks behavior compatibility.
+
+
+GH-81746
+--------
+Validate extension JSON: API was removed: classes/EditorSceneFormatImporterFBX
+
+Renamed to EditorSceneFormatImporterFBX2GLTF.
+
+The compat breakage was deemed necessary as this is a class most users wouldn't
+use directly, and the name needs to be disambiguated with the new
+EditorSceneFormatImporterUFBX.