LibOverride: Add support for rotation mode of PoseBones.

Request from the studio.

source/blender/makesrna/intern/rna_pose.c

@@ -1142,6 +1142,7 @@ static void rna_def_pose_channel(BlenderRNA *brna)
 
   prop = RNA_def_property(srna, "rotation_mode", PROP_ENUM, PROP_NONE);
   RNA_def_property_enum_sdna(prop, NULL, "rotmode");
+  RNA_def_property_override_flag(prop, PROPOVERRIDE_OVERRIDABLE_LIBRARY);
   RNA_def_property_enum_items(prop, rna_enum_object_rotation_mode_items);
   RNA_def_property_enum_funcs(prop, NULL, "rna_PoseChannel_rotation_mode_set", NULL);
   /* XXX... disabled, since proxy-locked layers are currently