Geometry Nodes: Add Self Object Node

From the nodes' description: "Retrieve the object that contains
the geometry nodes modifier currently being executed". This was
discussed in the most recent geometry nodes module meeting.

Because the node allows you to retrieve the position of the modifier
object, it has to add a depsgraph relation to object transform.
Expect that modifiers will be reevaluated when moving the object.
In the future, better static analysis of node trees could make this
check smarter.

Differential Revision: https://developer.blender.org/D16037

source/blender/modifiers/intern/MOD_nodes.cc

@@ -203,6 +203,9 @@ static bool node_needs_own_transform_relation(const bNode &node)
     return storage.transform_space == GEO_NODE_TRANSFORM_SPACE_RELATIVE;
   }
 
+  if (node.type == GEO_NODE_SELF_OBJECT) {
+    return true;
+  }
   if (node.type == GEO_NODE_DEFORM_CURVES_ON_SURFACE) {
     return true;
   }