Switch `Tx` to a data family.

[lehins]

Unlike #4999, Tx has changed only twice, since shelley: ShelleyEra and AlonzoEra. Therefore this ticket will likely add a little bit more boiler plate. However, it will be very useful, since it will allow us to get rid of superficial newtype wrappers around the Tx in a whole varieties of places:

During translation in ledger:

• cardano-ledger/eras/alonzo/impl/src/Cardano/Ledger/Alonzo/Translation.hs

  Line 74 in 4962396

  newtype Tx era = Tx {unTx :: Core.Tx era}

• cardano-ledger/eras/babbage/impl/src/Cardano/Ledger/Babbage/Translation.hs

  Line 64 in 4962396

  newtype Tx era = Tx {unTx :: Core.Tx era}

• ...

In consensus:

• https://github.com/IntersectMBO/ouroboros-consensus/blob/2ae2fe7375d832a273817573235c791e7572e065/ouroboros-consensus-cardano/src/shelley/Ouroboros/Consensus/Shelley/Eras.hs#L363

There is probably some more that I am missing.