1. _gen_unique_bone_name(Ref<GLTFState> state, const GLTFSkeletonIndex skel_i, const String &p_name) won't return an empty string.
2. String GLTFDocument::_sanitize_bone_name(const String &name) will keep Japanese characters. Like: "全ての親".
3. The sanitize function allows the bone name to be not just alphanumeric. The only required conditions are the ones in add_bone.
> ERR_FAIL_COND(p_name == "" || p_name.find(":") != -1 || p_name.find("/") != -1);
(cherry picked from commit 7b76f8783f)
