Fix: set default bone collection active

Bone collection added by default along with the armature is not marked
as active. Visually this looks active but actually it's not (hover over the
properties like remove/move)

Also, when a new collection is added, mark that collection active.

Pull Request: https://projects.blender.org/blender/blender/pulls/111733

source/blender/blenkernel/intern/armature.cc

@@ -87,6 +87,7 @@ static void armature_init_data(ID *id)
   /* Give the Armature its default bone collection. */
   BoneCollection *default_bonecoll = ANIM_bonecoll_new("");
   BLI_addhead(&armature->collections, default_bonecoll);
+  ANIM_armature_bonecoll_active_set(armature, default_bonecoll);
 }
 
 /**

source/blender/editors/armature/bone_collections.cc

@@ -87,7 +87,8 @@ static int bone_collection_add_exec(bContext *C, wmOperator * /* op */)
   }
 
   bArmature *armature = static_cast<bArmature *>(ob->data);
-  ANIM_armature_bonecoll_new(armature, nullptr);
+  BoneCollection *bcoll = ANIM_armature_bonecoll_new(armature, nullptr);
+  ANIM_armature_bonecoll_active_set(armature, bcoll);
 
   WM_event_add_notifier(C, NC_OBJECT | ND_POSE, ob);
   return OPERATOR_FINISHED;