Cleanup: Remove runtime node flag, various node transform cleanups

Remove another runtime node flag that's simpler as a local variable.
Use references, C++ types, simpler for loops, etc.

source/blender/editors/include/ED_node.hh

@@ -2,6 +2,7 @@
 
 #pragma once
 
+#include "BLI_vector_set.hh"
 #include "ED_node.h"
 
 struct SpaceNode;
@@ -11,6 +12,8 @@ struct bNodeTree;
 
 namespace blender::ed::space_node {
 
+VectorSet<bNode *> get_selected_nodes(bNodeTree &node_tree);
+
 void node_insert_on_link_flags_set(SpaceNode &snode, const ARegion &region);
 
 /**