Geometry Nodes: support muted nodes

The handling of muted nodes is handled at the derived node tree
level now. This is also where expanding node groups is handled.
Muted nodes are relinked and removed from the derived tree
during construction. The geometry node evaluation code does
not have to know about muted nodes this way.

source/blender/nodes/function/node_function_util.cc

@@ -27,4 +27,5 @@ void fn_node_type_base(bNodeType *ntype, int type, const char *name, short nclas
 {
   node_type_base(ntype, type, name, nclass, flag);
   ntype->poll = fn_node_poll_default;
+  ntype->update_internal_links = node_update_internal_links_default;
 }