Fixing return ordering of depth_first_traversal_by

Summary:
The original is D57905416.
`preorder-left-to-right` by default was backed out D58097382 due to runtime failures. Investigation showed that it was not implemented correctly.
`depth_first_traversal_by` does two things:
1. Calls `get_nodes_to_traverse_func` for each node. That was called with correct `preorder-left-to-right` order as expected.
2. Returns the list of all elements that was walked throught. **We had an error here**. We can't use `visited` list for returning results. `visited` does *not* always ordered in the same way. If we have more than one `roots` passed the order was broken.

Solving it by defining explicit list for return and fill it in the exact same way I do traversal. Now everything works!

Reviewed By: artempyanykh

Differential Revision: D58137945

fbshipit-source-id: 53aacdd3b833de48e7e91e01a2ef10fefee81252

utils/graph_utils.bzl

@@ -201,7 +201,7 @@ def depth_first_traversal_by(
         graph_nodes: [dict[typing.Any, typing.Any], None],
         roots: list[typing.Any],
         get_nodes_to_traverse_func: typing.Callable,
-        traversal: GraphTraversal = GraphTraversal("preorder-right-to-left"),
+        traversal: GraphTraversal = GraphTraversal("preorder-left-to-right"),
         node_formatter: typing.Callable[[typing.Any], str] = str) -> list[typing.Any]:
     """
     Performs a depth first traversal of `graph_nodes`, beginning
@@ -216,6 +216,7 @@ def depth_first_traversal_by(
 
     # Dictify for O(1) lookup
     visited = {k: None for k in roots}
+    result = []
     stride = -1 if traversal == GraphTraversal("preorder-left-to-right") else 1
 
     stack = []
@@ -226,6 +227,8 @@ def depth_first_traversal_by(
         if not stack:
             break
         node = stack.pop()
+        result.append(node)
+
         if graph_nodes and node not in graph_nodes:
             fail("Expected node {} in graph nodes".format(node_formatter(node)))
         nodes_to_visit = get_nodes_to_traverse_func(node)
@@ -237,4 +240,4 @@ def depth_first_traversal_by(
 
     expect(not stack, "Expected to be done with graph traversal stack.")
 
-    return visited.keys()
+    return result