Update on "support back propagate debug handle to arbitrary ancestor export graph"

Currently propagate_back_debug_handle function can only support propagating debug handle back to the greatest ancestor export graph.
This diff update algo to support every possible ancestor export graph on the flow.

Differential Revision: [D78464992](https://our.internmc.facebook.com/intern/diff/D78464992/)

[ghstack-poisoned]

Author: Gasoonjia