Sculpt: Simplify BVH node flag initialization, avoid normals update

Use the default constructor of `Node` to set the default new flag value.
Remove the normals update flag which was added in f9c6fe30db.
This should avoid recalculating all the normals after just building the
BVH tree.

source/blender/blenkernel/BKE_pbvh_api.hh

@@ -137,7 +137,8 @@ class Node {
 
   /* Indicates whether this node is a leaf or not; also used for
    * marking various updates that need to be applied. */
-  PBVHNodeFlags flag_ = PBVHNodeFlags(0);
+  PBVHNodeFlags flag_ = PBVH_UpdateBB | PBVH_RebuildDrawBuffers | PBVH_UpdateDrawBuffers |
+                        PBVH_UpdateRedraw;
 
   /* Used for ray-casting: how close the bounding-box is to the ray point. */
   float tmin_ = 0.0f;

source/blender/blenkernel/intern/pbvh.cc

@@ -209,9 +209,6 @@ static void build_mesh_leaf_node(const Span<int> corner_verts,
       }
     }
   }
-
-  BKE_pbvh_node_mark_positions_update(&node);
-  BKE_pbvh_node_mark_rebuild_draw(&node);
 }
 
 /* Return zero if all primitives in the node can be drawn with the
@@ -267,7 +264,6 @@ static void build_nodes_recursive_mesh(const Span<int> corner_verts,
       node.flag_ |= PBVH_Leaf;
       node.prim_indices_ = prim_indices.as_span().slice(prim_offset, prims_num);
       build_mesh_leaf_node(corner_verts, corner_tris, vert_bitmap, node);
-
       return;
     }
   }
@@ -464,10 +460,7 @@ static void build_nodes_recursive_grids(const Span<int> grid_to_face_map,
     {
       Node &node = nodes[node_index];
       node.flag_ |= PBVH_Leaf;
-
       node.prim_indices_ = prim_indices.as_span().slice(prim_offset, prims_num);
-      BKE_pbvh_node_mark_positions_update(&node);
-      BKE_pbvh_node_mark_rebuild_draw(&node);
       return;
     }
   }

source/blender/blenkernel/intern/pbvh_bmesh.cc

@@ -2189,9 +2189,6 @@ static void pbvh_bmesh_create_nodes_fast_recursive(Tree *pbvh,
 
     n->bounds_orig_ = n->bounds_;
 
-    /* Build GPU buffers for new node and update vertex normals. */
-    BKE_pbvh_node_mark_rebuild_draw(n);
-
     BKE_pbvh_node_fully_hidden_set(n, !has_visible);
     n->flag_ |= PBVH_UpdateNormals;
   }