Armature: Add minimal DNA defaults for bArmature.

Using mainly values used in `BKE_armature_add()`.

source/blender/makesdna/DNA_armature_defaults.h

@@ -0,0 +1,40 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup DNA
+ */
+
+#pragma once
+
+/* Struct members on own line. */
+/* clang-format off */
+
+/* -------------------------------------------------------------------- */
+/** \name bArmature Struct
+ * \{ */
+
+#define _DNA_DEFAULT_bArmature \
+  { \
+    .deformflag = ARM_DEF_VGROUP | ARM_DEF_ENVELOPE, \
+    .flag = ARM_COL_CUSTOM,  /* custom bone-group colors */ \
+    .layer = 1, \
+    .drawtype = ARM_OCTA, \
+  }
+
+/** \} */
+
+/* clang-format on */

source/blender/makesdna/intern/dna_defaults.c

@@ -109,6 +109,7 @@
 #include "DNA_volume_types.h"
 #include "DNA_world_types.h"
 
+#include "DNA_armature_defaults.h"
 #include "DNA_brush_defaults.h"
 #include "DNA_cachefile_defaults.h"
 #include "DNA_camera_defaults.h"
@@ -135,6 +136,9 @@
 #define SDNA_DEFAULT_DECL_STRUCT(struct_name) \
   static const struct_name DNA_DEFAULT_##struct_name = _DNA_DEFAULT_##struct_name
 
+/* DNA_armature_defaults.h */
+SDNA_DEFAULT_DECL_STRUCT(bArmature);
+
 /* DNA_brush_defaults.h */
 SDNA_DEFAULT_DECL_STRUCT(Brush);
 
@@ -288,6 +292,9 @@ extern const bTheme U_theme_default;
 /** Keep headers sorted. */
 const void *DNA_default_table[SDNA_TYPE_MAX] = {
 
+    /* DNA_arnature_defaults.h */
+    SDNA_DEFAULT_DECL(bArmature),
+
     /* DNA_brush_defaults.h */
     SDNA_DEFAULT_DECL(Brush),