Implement source maps between proto/document nodes

Add the node path to the document node and carry that over to the proto
nodes which are generated from that.
This pr also adds a compiler pass to assign the paths based on the
hierarchical structure of the nodegraph.

Test Plan: - Run units tests which check the path propagation works

Reviewers: Keavon

Reviewed By: Keavon

Pull Request: https://github.com/GraphiteEditor/Graphite/pull/1181

node-graph/graph-craft/src/executor.rs

@@ -10,6 +10,7 @@ pub struct Compiler {}
 impl Compiler {
 	pub fn compile(&self, mut network: NodeNetwork, resolve_inputs: bool) -> impl Iterator<Item = ProtoNetwork> {
 		let node_ids = network.nodes.keys().copied().collect::<Vec<_>>();
+		network.generate_node_paths(&[]);
 		network.resolve_extract_nodes();
 		println!("flattening");
 		for id in node_ids {