Add indents for all nodes in RenderTree.generateDebugString

Summary: When ``DuplicateRenderUnitException`` is thrown it is easier to debug when all nodes converted to strings have indents.

Reviewed By: pentiumao

Differential Revision: D65472834

fbshipit-source-id: c7a554ef6e40fa0f538c3917608e2f950171ffee

litho-rendercore/src/main/java/com/facebook/rendercore/RenderTree.kt

@@ -127,6 +127,7 @@ class RenderTree(
         append("RenderTree details:\n")
         append(String.format(l, "Full child list (size = %d):\n", renderTree.flatList.size))
         for (node in renderTree.flatList) {
+          append("  ".repeat(node.getHierarchyDepth())) // indent
           append(String.format(l, "%s\n", node.generateDebugString(renderTree)))
         }
       }

litho-rendercore/src/main/java/com/facebook/rendercore/RenderTreeNode.kt

@@ -81,6 +81,16 @@ class RenderTreeNode(
         parentId)
   }
 
+  fun getHierarchyDepth(): Int {
+    var depth = 0
+    var node: RenderTreeNode? = parent
+    while (node != null) {
+      depth++
+      node = node.parent
+    }
+    return depth
+  }
+
   companion object {
     private const val DEFAULT_SIZE = 4
   }