Avoid creating instances of nested procedurals that contain a single object

When we render an instance of a non-renderable primitive, we have to create a nested procedural. However, quite frequently, we end up creating such a procedural for a procedural that will create a single node. In that case we should manage to use this leaf node as the actual prototype for our instance

No source file or test is named. Start by tracing how instances of non-renderable primitives create nested procedurals, then identify the path that produces a single node; done means that leaf node is used as the instance prototype without creating the extra procedural, with rendering behavior preserved.

Written by the indexing model from the issue text.