feat: Add VRM Blender addon with complete import/export functionality

- Add core VRM addon infrastructure with manifest and registration
- Add common utilities module with file system, logging, and conversion helpers
- Add human bone mapper with support for multiple rigging standards (Mixamo, MMD, Unreal, Rigify, etc.)
- Add VRM 0.x and 1.x format support with property groups and handlers
- Add editor UI panels for VRM metadata, spring bones, and MToon materials
- Add exporter with glTF2 extension support for VRM format serialization
- Add importer with scene reconstruction and armature generation
- Add MToon shader support with auto-setup and material migration
- Add spring bone physics simulation with constraint handling
- Add node constraint editor for advanced rigging control
- Add comprehensive validation and error handling with user dialogs
- Add scene watcher for real-time property synchronization
- Add workspace management and preference system
- Include Python cache files and Blender manifest configuration
- This is the initial commit establishing the complete VRM addon ecosystem for Blender

exporter/gltf2_export_user_extension.py

@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+import bpy
+
+from .abstract_base_vrm_exporter import AbstractBaseVrmExporter
+
+
+class glTF2ExportUserExtension:
+    def __init__(self) -> None:
+        context = bpy.context
+
+        self.object_name_to_modifier_names = (
+            AbstractBaseVrmExporter.enter_hide_mtoon1_outline_geometry_nodes(context)
+        )
+
+    # 3 arguments in Blender 2.93.0
+    # https://github.com/KhronosGroup/glTF-Blender-IO/blob/709630548cdc184af6ea50b2ff3ddc5450bc0af3/addons/io_scene_gltf2/blender/exp/gltf2_blender_export.py#L68
+    # 5 arguments in Blender 3.3.0
+    # https://github.com/KhronosGroup/glTF-Blender-IO/blob/92061fa5b8058c8dff964c9bf177e079926b9671/addons/io_scene_gltf2/blender/exp/gltf2_blender_export.py#L85
+    def gather_gltf_hook(
+        self,
+        # The number of arguments and specifications vary widely from version to version
+        # of the glTF 2.0 add-on.
+        _arg1: object,
+        _arg2: object,
+        _arg3: object = None,
+        _arg4: object = None,
+    ) -> None:
+        context = bpy.context
+
+        AbstractBaseVrmExporter.exit_hide_mtoon1_outline_geometry_nodes(
+            context, self.object_name_to_modifier_names
+        )
+        self.object_name_to_modifier_names.clear()