Update on "[FX] Fix submodule naming for subgraph split"

Submodules copied into a partition were using only the last atom in the qualified name, which caused problems when different Modules with the same last atom are put into the same Partition. Use the full qualname with underscores instead

Differential Revision: [D24925283](https://our.internmc.facebook.com/intern/diff/D24925283)

[ghstack-poisoned]

test/test_fx_experimental.py

@@ -538,7 +538,7 @@ def test_subgraph_trivial_resnet(self):
         m = resnet18()
         traced = symbolic_trace(m)
         a = torch.rand(64, 3, 7, 7)
-        module_with_submodules = split_module(traced,m,lambda node: 0)
+        module_with_submodules = split_module(traced, m, lambda node: 0)
         module_with_submodules(a)
 
     def test_traceable_function_with_nonstandard_name(self):