Make TPU variable name deterministic.

Only use the unique variable handle id as handle cache key, but not the variable handle's name.

This resolves a graph non-determinism issue seen in an internal workload.

PiperOrigin-RevId: 436262849

Author: chuanhaozhuge

mesh_tensorflow/tpu_variables.py

@@ -82,7 +82,9 @@ def handle(self):
     if tpu_context is None:
       return self._primary_var.handle
 
-    return tpu_context.get_replicated_var_handle(self._name, self._vars)
+    # Using variable name as handle id.
+    return tpu_context.get_replicated_var_handle(self._name, self._name,
+                                                 self._vars)
 
   @contextlib.contextmanager
   def _assign_dependencies(self):