Clean up the build_xla_ops to use the generated C++ TF op wrappers.

This cleanup will make the future CL implementing lazy compilation simpler.

Includes some supporting changes:

 - Teach NewInternalScope to create a scope that doesn't do shape inference.  We
   need this because we don't have a ShapeRefiner that has been run over the
   entire graph available in the build_xla_ops pass.

 - Add a WithAssignedDevice modifier to tensorflow::Scope.

 - Make cc_op_gen write out an Operation field for nodes which may not
   necessarily have any outputs.  We already did this in most cases, but we
   weren't doing it for nodes that have possibly-empty list outputs.

 - Minor change renaming ops/xla_jit_op.cc to ops/xla_jit_ops.cc, now that we
   have more than one XLA JIT op.

PiperOrigin-RevId: 215293817