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

common/char.py

@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+from collections.abc import Mapping
+from typing import Final
+
+INTERNAL_NAME_PREFIX: Final = "\N{FULLWIDTH BROKEN BAR}"
+"""
+The letter to be prefixed when naming internal invisible objects. It was chosen so that
+the sort order would be backward and also so that it would be easy to identify the
+object as internal.
+"""
+
+DISABLE_TRANSLATION: Final = "\N{ZERO WIDTH SPACE}"
+
+FULLWIDTH_ASCII_TO_ASCII_MAP: Final[Mapping[str, str]] = {
+    chr(ascii_char + 0x0000_FEE0): chr(ascii_char) for ascii_char in range(0x21, 0x7E)
+}