Wrap HloPass in Pass automatically

[iamohcy]

As the Pass interface we use for our Pipeline differs from Xla's Pass Interface, we defined both our own Pass class which wraps XLA's HloPass class via pybind11. However this leads to confusing code where we have to wrap each HloPass in a Pass, e.g.:

fusion_pass = Pass(hloenv.HloPass.GeneralFusionPass())

It would be preferable to wrap it dynamically so we can just call

fusion_pass = hloenv.HloPass.GeneralFusionPass()