[mhlo] Remove tuple from mhlo whileOp
[mhlo] Remove tuple from mhlo whileOp

This includes the following changes
 - Importing XLA HLO --> MHLO
 - Exporting MHLO --> XLA HLO
 - Legalizing tf control from during legalization from tf --> MHLO
 - Fixing the legalization of custom tf ops
 - Lowering Tensorflow dialect's communication ops to MHLO
 - Jax lowering to MHLO
 - MHLO's legalize control flow pass

PiperOrigin-RevId: 417534873

google/jax,google/jax,google/jax,google/jax