Discover trainable parameters using reverse DFS from loss node (#4116)
Discover trainable parameters using reverse DFS from loss node, omitting recursion along untrainable inputs.
Co-authored-by: suffian khan <sukha@OrtTrainingDev4.af05slrtruoetgaxwwjv5nsq5e.px.internal.cloudapp.net>
Co-authored-by: suffian khan <sukha@microsoft.com>